Different times, different reasons...

I mainly ride with DH. When I say ride with DH, I mean drive to the trail together, start trail together, he drops me, we meet up at the end. If it's a longer trail, he'll wait for me every few miles.

I enjoy this because I know someone will be know if I get hurt, someone is there to motivate me when I'm tired, someone is there for the pre-ride talk and the talk on the drive home. When he rides behind me, it helps push me to take the downhills a little faster.

Also, I would never ride offroad at night by myself. That feels way too unsafe to me. I don't think I would even show up to a random group ride at night unless I personally knew someone on it.

I like to ride with other people (not DH) sometimes to compare myself, sometimes for social rides, and also to motivate some of my friends to try riding.