The key to swimming quickly, effectively, and powerfully is to optimize balance in the water while minimizing drag. This is exactly what occurs when swimmers submerge their hips in water. They are increasing their drag and hence slowing down. This is why coaches call this movement "floating" or "hip-deep diving." Keeping your head above water is important for several reasons. First of all, it allows you to breathe easily. With your face under water, you would need to constantly resurface to take a breath, which would be difficult at best and impossible at worst. Keeping your head above water also gives you a better view of what's going on around you, which can help you avoid obstacles and avoid being hit by other swimmers or boats. Finally, keeping your head above water helps you maintain control. If you were staring at the bottom of the pool with only your toes poking out of the water, you wouldn't be able to steer yourself properly toward one side or another. As long as you have your head up, you can continue to glide along without difficulty. Overall, balancing needs and skills must be developed through practice. Swimming is not only about getting from A to B but also about having fun! That said, practicing proper form is essential for achieving good results without hurting yourself.