I think it depends. I think some are perfectly fine without a friend, and some do much better with one. As LBJ said, some are more dependent or independent. It’s not absolutely necessary and with human interaction bunnies live a perfectly happy life. Bonding is also pretty stressful (on human and rabbits) so it’s not something to take on lightly. There were days when I spent 4 hours bonding and hated every minute of it – I was unemployed and can’t imagine finding the time to do that with a full time job.
If you want another rabbit, make sure you’re ready for the increase in cost and care, and be prepared for a long bonding period, or for them to not bond at all.
I will say that it’s so much fun to watch them interact, and they really do get joy from one another. I have an independent holland lop boy who didn’t really need a friend, and a dependent mini lop girl who desperately wanted a friend. My boy would have been just fine on his own, but it does make me feel better to know that he has a buddy when I’m not home or able to spend time with them.