The QL tends to get tight very easily. Something as simple as sitting for a couple of hours can cause tightness in the muscle, which can cause low back pain and discomfort.

The QL is key for stabilizing the low back and the pelvis (hence the discomfort when it gets tight).

It also helps with maintaining good posture and side-to-side bending. You can think of your QL muscle as the stabilizing ropes in a suspension bridge.