We have a wealth of questions about cross-validation, such as
Which are, if not identical to eachother, do overlap by about 80%. Recently, someone asked the question
Which would seem to overlap with each of those previous threads substantially. The author expressed doubt about many of the threads that I linked to, but I'm not sure that the author's doubt is a great reason to open a new thread which covers highly similar, if not identical, ground as previous threads. This is the same reason we have one canonical thread on the coupon-collector problem, not a separate one for each type of collectible item in existence.
Or, we might look at this from the opposite perspective and say that we have a scattered collection of threads about how cross-validation is used and the problems it does (and doesn't) solve -- but no single, coherent, authoritative thread about cross-validation. I can see two ways to make CV better and more accessible in this regard:
With malice aforethought, compose a question which fills in the interstitial gaps in our existing questions about CV, and then answer that question deliberately and authoritatively.
Consolidate existing threads to form a one-stop (or perhaps two-stop) shop of answers about cross-validation.
I personally favor option 2, since lots of the work has already been done to lay the groundwork of what CV is. Option 1 will create yet another thread about cross-validation and will be harder to find unless it's highly up-voted immediately or you're the Rain Man of the search feature.