What exactly does adding someone as a friend do?

Hello,

Sometimes I receive friend requests that I am unsure if I should accept. For me in many of these cases, the determining factor is what exactly accepting them as a friend does. Is it purely symbolic + the no-common-sever-DMs thing, or does it do something else too? If so, what?

To ensure that I accidentally don't release any data to someone I don't want to have it (ie. my server list), I would appreciate a link to some sort of source if you're answering and aren't a Discord employee who knows 100% for sure.