Pro tip: check for crown before you cut that upper cabinet run, or you'll be pulling a whole run in Boise
Last month I was hanging uppers in a 1950s rental in Boise and got six boxes up on the rail before I noticed the ceiling was out almost 7/8 inch across the run. I could shim the top rail and let the crown eat the gap, or pull it all and scribe a filler strip. I pulled it, lost half a day, and the homeowner told me later the old cabinets had the same gap because a previous guy just caulked it. That caulk job was cracking and ugly, so I feel okay about the call. But now I'm second guessing mysit because a buddy swears shims plus a deeper crown always looks cleaner and nobody looks up there. So which is it, do you shim and hide it or pull and scribe every time? Curious what the trim carpenters here would do.
Seven-eighths of an inch over a run that long is a lot, and I say that as a guy who once caulked a gap so wide it looked like a smile. My rule is shims plus crown only when the gap is small and even, maybe a quarter inch at most, and when the crown is deep enough that it really does cover. A wavy 7/8 gap has to get pulled and scribed, because shims will get you level but they leave the wall line looking drunk from the side. Your buddy is right that nobody looks up there on a normal day, but bad work has a way of finding the one person who does. Losing half a day stings, but you can't un-see a gap once it's caulked and cracking.