Google currently offers YouTube users the option of either using their G+ profile or a YouTube profile.
I tried the G+ profile option for a while, but I didn't really like it. The first time I posted something publicly, people started commenting on my Google+ posts, apparently upset because they did not get the joke I made. Someone in the YouTube comments looked up my profile, figured out where I lived, and threatened to come to "BrookLine New York" to adjust my viewpoint. I found it hilarious but most people would probably be scared.
I switched back to using a real-name-inspired nickname. You blend in better and people won't bother you except in comment replies, which you can easily ignore.
From Google's point of view here there is only gain--YouTube comments are some of the lowest form of internet communication to be found. App reviews are not much better. Requiring people to have some sort of profile is not going to lower the quality of reviews, it will only limit their quantity (which is not the lacking factor).