It varies massively and is very dependent on the type of community and the existing ethos.
That said, as with a lot of community initiatives: just try it 
The best way that I’ve seen them work is if the community manager actively invites people into the community to introduce themselves. This is one of those repetitive tasks that you shouldn’t automate, give it some flair, hook into someone’s name or bio or whatever. If it’s holiday season make it a rhyme etc.
They can be a great tool to get people to participate and step out of the lurker or one-time-participant vibe.
They can also fizzle and not work at all, which you’ll know after a few tries.