High rep workouts aren't an excuse to use bad form. There are few things more important in the fitness world than doing an exercise correctly. It's key to targeting the intended muscle group, and it's a vital component of injury prevention [source: Stefano]. The lighter weight associated with high rep workouts should make it easier for you to use a full range of motion whether you're doing squats, dead lifts, curls or any other exercises.
But there's a danger in associating high repetitions with high speed. If you're doing an exercise so quickly that you end up swinging, jerking and flailing about, you're asking for an injury. Doing 20 repetitions properly is more important than completing 20 repetitions fast.