In a previous question I asked what I need to know about turbo trainers, but several answers mentioned the use of rollers. What are the pros and cons of turbo trainers and rollers?
Turbo trainers allow you to alter the resistance, so they are good for interval style workouts. They don't require any skill to use as you're locked in place. But as most people will tell you, riding a turbo trainer gets very dull very quickly, and unless you really concentrate they don't do much for your "souplesse" (spinning smooth circles at a high cadence, the most efficient way to pedal) - it's easy to just stomp up and down on the pedals.
Rollers require you to balance and it takes a little to get used to them. On some models you can't alter the resistance, although you can of course shift into a higher gear to work harder. It's generally accepted that they are very good for your souplesse, in part because pedalling smoothly makes it easier to balance. They are also a lot less dull than a trainer - you can even get fancy sets of rollers that allow you to stand up and pedal.
Ideally you'd want both - a turbo trainer for shorter, intense interval style workouts against resistance to build speed and power, and rollers for spinning smoothly for longer periods of time to get in the miles and build endurance.
I would argue that there are few advantages to the trainers other than ease of use. Chris B's answer that an advantage of a trainer is the resistance is not valid since it is possible to change the resistance on rollers either by using a similar attachment like a magnetic wheel, or by using rollers with a smaller diameter.
Advantages to rollers:
- improve bike handling skills
- improve pedaling efficiency
- riding rollers is an impressive skill in and of itself
Disadvantages to rollers:
- Steep learning curve. Best to start in a doorway or next to a counter. However, parabolic rather than flat rollers make it easier to learn. See the answer to this question
Advantages to a trainer:
- easy to use
- holds your bike up when you get off
Disadvantages to trainers:
- clamping in the rear hub and pedaling hard stresses the bicycle frame
- can leave a flat spot on or all the way around your tire
- can spray rubber from tire onto carpet