Rollers are great for building balance and an efficient pedal stroke. The negative is that they take a little while to master as there's nothing holding you up - especially tough when getting going.

That said, I still prefer rollers to a trainer because it takes some of the monotony out of riding inside. If you lose too much concentration while riding the rollers, you very well could fall and injure yourself (and/or your house)!

As for me, unless it's truly miserable outside - rain/snow/ice and bitterly cold temps (the teens and under) I also prefer to bundle up and ride through it...