Stable environment, safe, done properly can improve balance, help prevent falls, back pain, knee pain, hip pain, sprained ankles, etc
Can be done for repetitions or held for time. Start with 2 sets of ten with a one second pause at top and progress from there.
Once mastered can be progressed to marching in place, single leg kick outs, and then single leg glute bridges as all shown in video
This exercise when done properly is felt in the buttocks and not low back or back of legs. Always brace thru the core and squeeze your glutes to ensure that you feel the exercise in the right place.