Danaher says:

Learn to get comfortable in inverted positions on your shoulders and double the number of submission entries you can attempt: When we first start jiu jitsu we all learn the fundamental attacks from bottom guard positions with our head far away from our opponent and our hips closer to the opponent than your head. That is sensible because Jiu jitsu evolved as a fighting style and in a fight it’s generally wise (especially at beginner level) to keep your head as far away from an opponents fists and elbows as possible. This does rather limit your submission entries however. In a sport context where strikes are not an issue, inversion under your opponents upper body with your head closer to your opponent than your hips suddenly opens up a vast new set of submission entries from unexpected angles. Because your legs are unweighted in these scenarios, they move quickly and easily into attacks. Here, Nicky Ryan inverts Unser brother Gordon to enter into triangles, arm bars, omoplatas. He could also easily go downstairs into leg locks. Learning to get comfortable in these inverted positions is a big part of your development in the bottom submissions game. Time spent getting yourself to relax and breath freely in positions like this will make you able to spin like a top under a tough opponent and whip your legs into attacks that can turn a match around in a second.