I agree, it removes surprise element as well as - people that know you would know what to buy you, people that don't know you shouldn't be buying you gift anyway.
I didn't. I created account for some integration in work started getting tons of invites. Eventually stopped using it nearly years ago. Not missing it at all!
The idea is that for example you like service provider (gym, dentist), you want to keep coming back, but you want to let them know about something that's bugging you - noisy music, messy office, toilets etc. I got feedback from some people where their issues were resolved.
When it comes to bosses ... I just can't imagine it working unless you have 10 or more people on the team. You can't discuss particular situations because your identity would be revealed. But that's me, I wish you good luck