Re: Backward Roll - Risks and benefits
In our dojo, we practice back rolls. I agree with the many posts here: it's primarily a training exercise. I also agree (as others have already said) that experienced nages rarely give their ukes the opportunity to do a back roll.
I don't find back rolls dangerous in and of themselves; however, there is one practice that I dislike: the use of back rolls as a "lazy" way of getting up from a fall. I've seen many aikidoka use a back roll where a back fall would do. Their reasoning is that it allows them to use some of the momentum from falling to stand back up. The problem I have with this is that, too often, they try to use a back roll in a situation that is unsafe. Some examples: they might be close to the edge of the mat, or they don't see that there are other students directly behind them.
I see no problem with using them as a training exercise or as another "tool" to add to one's ukemi skills. And they are pretty fun!