We do this quite a lot out of necessity. We have kids who are old enough to ride some things with an adult, but one who's too small to ride at all. One rides with the kids, and one stays behind with the little guy. When the first group is done, the second parent usually rides so we'll all be able to talk about it. And then there are the rides that we just aren't sure if the kids will be OK on them - one of us needs to ride first to be able to make a judgement call. And since we've had to do this quite a lot over the years, we've just become OK with riding something by yourself.
I've actually discovered a big advantage to it. At the parks around here (not DW), there will often be long lines for rides. But if you watch, there will sometimes be a single seat that no one takes. I've often asked people in front of me if they mind if I take that seat, since I'm riding solo. No one has ever minded, and I've hopped on rides MUCH FASTER than if I'd waited.
