One complaint I had about lash extensions was that, depending on your tech, your lashes can end up looking heavy and separated into clumps, if too many extensions are placed, it can weigh down the lashes. With a lash lift, your natural lashes are enhanced to look longer because they are curled upward.
Extensions provide a similar effect, but with lifts, you don't have to worry about heavy, clumpy lashes. This curled effect is especially great for the outer corners of your lash line, which can also create an overall lifted look for your eye.