Profiles provide isolation at the browser level, containers at the origin/domain level. Different profiles are essentially different browser installations that share nothing more than core browser code: extensions, settings, and even looks. It can get tedious to have to replicate one's browser customisations in every profile. Containers bring convenience.

I never made a separate browser profile for Facebook, but the moment Firefox's Containerisation was available in Test Pilot, I made a container for all things Facebook.

Depends on if you prefer separate windows or just separate tabs. I prefer having a single window and I've become so used to containers that using Private Browsing feels weird because I can't move those tabs into the main window.