Trainer tire also grips the metal roller better so it doesn't slip as much. That means that you don't have to tighten the roller against the tire as much, which is probably better for your wheel, and the tire won't slip as much when you are doing things like interval work or sprints where you apply a large amount of power to the wheel quickly. I have a dedicated wheelset for trainer/rollers that I bought from performance bike for like $200 and you probably can find some take offs from friends for cheap too. I even use a trainer tire on the front for rollers for the same reason. Grip the metal better, the rubber compound was designed for that, as opposed to a road tire that was designed to grip road.