It seems to me that you have 2 choices in any situation when you are about to make close aquaintance with the mat - go with the motion and roll out back to a standing position, or disperse the energy by flattening the body.
It depends on each individual situation. If there is not much momentum, or you are travelling some distance horizontally, a roll will usually present itself as the best option. If you get dropped much more vertically, or there is so much momentum that you will still be stumbling after the roll, a breakfall will be the safest option.
Obviously if you are stiff or tense when taking a breakfall you run the risk of injury.
A couple of years ago I was told that I was helping my tori too much much by 'jumping' for them - preempting their technique. The next technique after that I stayed totally relaxed, and basically let my body be moved wherever tori wanted it to go. The resultant breakfall was much louder than any before, but the feeling of hiting the mat was if anything softer.
There is definately a difference between stiffening up and being able to stop dead as one mass on the mat, and louder doesn't mean worse. I suppose it's just a matter knowing the best response to whatevers thrown at you (or what your thrown at!!)