Smartphones usually have QuadBayer arrangements, so the MP in the final picture is much lower than the nominal (advertised) value.
Regarding MP count at large, I find that there has to be a balance between camera MP count, interface/card/mass storage transfer speed, HDD size and cost, CPU processing speed/RAM cost/performance and software speed in general.
All or most of these factors need to be aligned at reasonable values, otherwise the whole Jenga tower collapses.
With 8TB HDD being cheap-ish, PCs being quite powerful, SD cards being big and cheap, many manufacturers implementing USB 3 in their cameras etc. I'm starting to feel like I manage with more than 16 MP per shot
24-36 looks like my personal sweetspot ATM, but it's largely a personal preference.
After all, if one doesn't print, you can't really have more than ~8 MP on screen at a time
For professionals it's another story entirely, obviously.