Hi Sharon!
Low Ends are working on a few things actually.
#1) Varying the way you spend your time under tension recruits muscle fibers in different ways, therefore stimulating and challenging muscle fibers in different ways. Simply put, keeps the muscle shocked.
#2) Both strength gains and endurance gains are received when doing Low Ends. Much will depend on how much weight you use (Side Note: Keep in mind, low ends should not be done with a VERY heavy weight since it is a lot of pressure on the lower back). Spending more time in the "work zone", the portion of the exercise where the muscle is most challenged, will provide more strength gains initially. As the muscle adapts to this particular workout pattern, the strength gains will lessen and endurance gains will increase, unless slightly more resistance is added (see side note above)
#3) Low End Squats and full range squats are both a very important part of your workout program. You should always include working your muscles in full range of motion to "keep" their full range of motion. Constantly training muscles in short reps and never opening up to full range of motion could eventually decrease your muscle's length, flexibility and capability to perform at its full capacity.
Take Care