Hips are crazy. If they get tight, your femur bone twists slowly and doesn’t align correctly with your shin, which then cause major knee pain. So, you always want your hips to be as flexible as possible. Also, you want your hip flexers to be loose so that you can actually do military press standing without fucking with your back hard. Hips are very important. So many things get fucked up when the hips aren’t flexible. Your squatting will hurt your back (because of butt wink) if your hips are tight. For squatting to be healthy, you need to have flexible hips and loose Achilles tendon.