As Eisenhower put it: "Peace-time plans are of no particular value, but peace-time planning is indispensable."
In other words, the act of planning means you're better prepared for specific contingencies, so you'll hopefully be better prepared for whatever actually happens, but some improvisation will always be necessary.
100%. As another wise man once said, "everybody has a plan until they get punched in the mouth."
The planning may be directly applicable in whole, is almost certainly applicable in part but in my opinion the main thing is that it provides a template for thinking about what things are important and which are expendable when you're operating in an environment with a greater tolerance for risk.
In other words, the act of planning means you're better prepared for specific contingencies, so you'll hopefully be better prepared for whatever actually happens, but some improvisation will always be necessary.