15" late 2013 MBP: 1) What downsides to upgrading without wiping the SSD? 2)How to keep already installed Boot Camp partition?

Hi, I've got a 15" Retina MBP from late 2013 (macbookpro11,3) with a 2TB drive. I've got Big Sur installed with programs and data, but I also have a Boot Camp Windows 10 partition with programs and data on it.

I've been following the discussions and videos, but I'm pretty confused. I want to use OCLP to go to Sonoma. I think I understand how, but the usual recommendation is to wipe the drive first and then use Time Machine to reinstall your programs and data. I understand it's possible to do it directly from Big Sur with OCLP, but that's frowned on - what exactly are the downsides to that approach, other than some superfluous files hanging around? Of course, I'll have the Time Machine backup in case anything goes wrong.

Secondly, I've got a boot camp (bootcamp) partition with Windows 10 and data and programs already installed. If I update to Sonoma, will I still have that partition intact and useable? If not, how do I approach backing up the Windows partition and reinstalling it after the Sonoma upgrade?

Honestly, I tried to find clear answers, but struck out. Thanks so much!