The vast majority of turbo trainers work by pushing your bikes back tyre against a roller on the trainer resistance unit. This roller is than connected to either a spinning fan/blade or a spinning disc. When you pedal you back wheel spins the roler which then spins the fan/blade/disc, which generates resistance.
There are a couple of issues with this setup. One is that your tyre generates friction and thus is wears. Depending on the trainer you have, how hard you workout, and how often you use your turbo trainer influences the amount of wear you get. Special trainer tyres can be bought to replace your normal tyre during workouts, but this adds extra hassle and also cost.
Another issue with these trainers is that sometimes you get slippage between your tyre and the roller. This can occur when you get out of the saddle and apply sudden forces to your bike, which will bounce your back tyre a little. This mean the force pushing down on the roller is sometimes reduce causing your tyre to slip slightly. This increases wear and also reduces the accuracy of your workout.
Direct-drive turbo trainers on the the other hand allow you to remove your back tyre completely and fix your folks directly to the trainer. This eliminates both the mentioned issues that occur with traditional trainers. Of course removing your wheel and fixing your bike to the trainer is more work, but once setup the ride will be better. This type of trainer is often used by professional cycling teams and serious indoor riders.
Browse the range of direct-drive trainers below: