Fournicator,
Whilst the barrel roll may be a simple manouvre to fly, it is also one which is easy to get wrong if you don't have the proper training.
The problem is the last half where the beginner often shows a tendency to stop the roll and try to pull through (or spiral dive) especially if the nose has already passed through the horizon.
The benefit of competition aerobatic training is the high discipline required. Whether you actually compete is a different matter much as you would still be a better swimmer for having a competition swimming coach. All in the technique.