The benefits of full range of motion include increase strength, increased joint mobility, larger, fuller muscle bellies and increased tendon and ligament strength. It is important to note though, to be careful not to hyper extend the joints when coming to the extreme extended position. It is not a good practice to "lock out" the weight bearing joint. When performing full range of motion reps, always observe proper form and complete the reps with a 2 count lifting,, pause for a 1 count and then lower the weight again with a 4 count. The American College of Sports Medicine suggest the 2-1-4 count rep has been proven to minimize joint and muscle damage by providing a controlled rep.
Next time you hit the gym, try doing full range of motion reps. Many of us generally don't go through a full range of motion when strength training. Give it a try... You're muscles will thank you!