Different goals require different approaches in the weight room. If you want to build bigger muscles, it's best to perform high reps with a moderate amount of weight. If you're out to get stronger, work with loads near your one rep max for only a few reps. A study published in the Journal of Electromyography & Kinesiology points out that muscles fatigue differently during each of these workouts.
In one session, researchers had subjects train for 5 sets of 10 reps with a relatively light load of plates. This caused peripheral fatigue and a noticeable decrease in force production. Lactate buildup was also greater for the hypertrophy session compared to the strength workout which involved 15 sets of 1 rep with a load equivalent to each subject's one rep max. That session had a greater effect on the central nervous system. Work both routines for maximum benefit.