Re: high breakfalls?
High breakfalls can be a necessity depending on the style you are in. That much is clear.
I think that anything that can help you out to prevent injury is good. Remember first rule of Budo!
Off course in many cases executing breakfall is a choice of aite, not imposed by tori. However sometimes tori can be very determined and have (total) control over you and then you must do breakfall do protect yourself. I do not think there is a clear border here...
As a teacher I spent a fair amount of time on ukemi (during aiki taiso) because students learn to control their body, increases confidence. I start with suwari waza ushiro ukemi (backwards roll from seated position), then mae ukemi (forward roll). Next tachi waza mae ukemi (forward roll from standing position).
When standing you first may use your arms, next round cross your arms, third round keep your arms to the side of your body. This sequence forces you to stay more and more centered while doing the same movement.
Another very useful exercise is rolling over someone seated (on all fours) on the floor.
A nice crossover exercise from forward fall to breakfall/freefall is koshinage as tori has very much control over aite and can prevent mishap quite easily. Compare this to e.g. kotegaeshi: when aite falls poorly, tori cannot do anything about it ;-(