I tend to be fastidious when reviewing, so only apply "No Action Needed" on about 20% of reviews (excluding skipped reviews). I wondered whether this was normal and having look at other reviewers, I found some apply "No Action Needed" to 80%+ of reviews.
I find it hard to imagine 80%+ of posts really need no action, based on what comes my way in the review queue. Of course, it's possible they apply the reverse strategy to me: skipping many posts with clear problems (maybe especially those that look hard to fix) and NANing the decent ones, whereas I tend to skip posts that look okay, superficially, but which I don't feel I can certify as "acceptable" since their content lies beyond my expertise. Or perhaps they see First Post review as little more than triage to weed out clearly poor or inappropriate content, so (if we imagine different "layers" of review we could perform) they may not take the review to quite the same level of depth:
- Appropriately flag
- content in a foreign language or patent nonsense
- "I am having this problem too" or "link only" answers
- Appropriately handle copy-and-pasted homework questions (if necessary inform about self-study tag, tell OP to show us where they are stuck, possibly vote to close in worst cases)
Clearly none of this material should survive First Post review, and all of this can be caught without subject knowledge expertise or even carefully reading through the post.
Requires effort but minimal expertise
- Remove salutations, thanks and signatures
- Fix spelling and grammar errors; formatting (particularly $\LaTeX$ and code formatting and indentation)
- Make title clearer and more specific if necessary
- Vote to close as unclear if a question is written in such poor English as to be indecipherable
This at least requires superficial engagement to read through the post's text, but not substantive expertise. I could perform all these actions without knowing anything about the topic of the post. Editing the title requires thought, but since OPs often pick one that's too generic, it might be improved simply by summarising the final point of their question.
Requires more expertise and/or more effort
- Adding relevant tags — so long as I can recognise the subtopic, then even if I know little about the area I can usually improve on the OP's tags: they rarely know which tags we have available. On questions I don't substantively understand, sometimes I can't even pin down the topic well enough to find a relevant tag (this is most frustrating when the one tag the question has is clearly irrelevant, and really should be replaced by something else).
- Checking for a duplicate question. This takes both effort (searching) and judgment (two questions might be presented and worded quite differently, but with the same core concept; it may take a degree of familiarity with the subject matter to identify that this is the case). I have a good memory for duplicates but rarely actively search for dupes unless I suspect one exists; perhaps I should be searching as a matter of course? In topics outside my area of expertise, I would struggle to identify whether two questions are duplicate or simply related (though this can be resolved by posting a link in a comment and letting more expert users identify whether this counts as a duplicate or not).
- Check a question contains enough information to answer it — this is often possible even if I wouldn't want to venture an answer. The simplest case is "could you include (a sample of) your data", while with probability questions we may need to clarify "are the variables intended to be independent" or similar. If the question clearly doesn't contain enough information, it may be necessary to vote to close it as unclear. But it is often the case that, outside my area of expertise, I have little idea whether a topic expert would regard the question as sufficiently clear to be answerable.
- Check an answer substantively addresses the question — even if I don't fully understand the answer (or indeed the question), it's generally possible, with a little familiarity with the topic, to ascertain whether an answer is at least germane to the question, and proposes some kind of solution. If not, it may be necessary to flag the question for moderator attention. If the answer is good, it should be upvoted, but I don't like doing this unless I understood (at least well enough to strongly suspect it's correct).
All of these require reading a question or answer closely and thinking in a critical and evaluative way about its content. The further its content lies from my sphere of knowledge, the less capable I am of performing this. Particularly when it comes to evaluating questions, perhaps these tasks are best handled by potential answerers, rather than reviewers.
Clearly reviews are multilayered, and we can't expect every reviewer to put total effort into every review, or only to review questions they are technically qualified to answer. On the other hand, CV is very fortunate that none of our review queues are Sisyphean tasks. If there is a post that lies outside our area of expertise, and there is no obvious issue to deal with, there seems no very strong reason (other than it adding one to our review queue score!) to say "superficially it looks okay, no action needed", if we could instead skip the review and have it passed on to a user with more (even if not masterful) topic expertise.
My philosophy generally has been "do what you can" — fix, flag or vote (up/down/close) — and if there is nothing (further) I can see to do, opt for "No Action Needed" (or "I'm Done") if I'm confident that the post is now good to go, but "Skip" if I think it would benefit from fresh eyes (perhaps even after my fixes). In many situations this means I get through the "requires effort but minimal expertise" before pressing Skip, and I will generally only NAN (or "I'm Done") if I reached the "requires more expertise and/or more effort" part of the checklist (though may not have done a full search for duplicates, completely understood an answer, etc). Is this an overly cautious approach? Should I feel I've "done enough" at a more minimal level of effort, and perhaps leave the rest for potential answerers to decide on? It certainly seems pointless (more work for everyone) to skip a post with no superficial flaws in the hope that the review will be "passed on" to someone with more subject expertise, if that post is then reviewed by someone who is only looking for superficial issues anyway. In this sense it would help if we were all reviewing to a somewhat comparable depth. Do my checklists leave anything important out? What's a realistic expectation for the depth of a review, particularly when you hit a post on the edge or even outside of your expertise?