You get no new advantages, can keep doing the same things (such as using the newest XCode) and all new disadvantages, like the Messages pop up in the upper right now takes 3 clicks to reply to because they collapsed the menu into “more” drop down. Now just extrapolate that to every pop up.

I got forced to upgrade to Big Sur recently and it’s working okay. The Lock Screen is my only issue. It flashes several times and makes me re-enter my password halfway through typing it