Rock climbing is a full body workout and in practice you can do whatever works best for you. Knowing how to use your arms and legs is important but so is knowing how to place your feet. We know that sometimes to go up we must look down to where there is an opportunity to push up from. What we are less likely to do is use the heel rather than the front of the foot for a foot hold.
When I was climbing this weekend I found that if I used the front of the climbing shoe I would slip. The person belaying me was giving instructions so I followed them. When I turned around and looked down though I saw that the person was giving instructions to someone else. I made the mistake of assuming that I was the one receiving directions. I benefited anyway. I tried different footholds and it worked. I felt safe and comfortable using my heel rather than the front of the foot. It was stable.
I mention this because in Villars sur Ollon at the IFSC Climbing World Cup you can often see climbers extend their leg horizontally and use the wall as a pressure point despite there being no foot holds.
In the second video produced by another person we see how hips can be used to counter balance movements and make reaching for hand holds easier. This is a technique I will need to practice in the climbing gym on the overhanging 6a routes. I know that I can do them but my fear of falling and my lack of trust that I have the strength limit me. If I practice this technique then I will climb to a higher standard.
Youtube videos are an excellent way of practicing skills and getting to the next level. There is always something new to learn, something that will make climbing less strenuous. This is a positive aspect of having a low barrier to entry for video content.