What does Omnisharp actually do?

[kuiperzone]

All I can find is that it adds "rich support", but don't know what that means or what Omnisharp actually does?

I've been using VS Code for years, sometimes with Omnishap and sometimes without. I don't notice any difference TBH, at least nothing I care about. Not being rude, just want to know why I would want it?

NB. The only reason I have it enabled is that some extensions need it.