The biggest reason for developing our kicking is to preserve the kinetic chain. Remember that your feet and legs are connected with your hands and arms. Also by kicking it allows us to engage our core and better utilize the rotational power of our hips. Lastly there are a lot of drills that require us to kick.
Second is we do not swim flat.
We swim from side to side ideally at a 45 degree angle to the bottom of the pool. The biggest reason for doing this is it allows us to couple rotational force with our pull. The majority of power in our swim comes from rotation. Rotating will reduce drag and help you to be longer in the water. I have also see so many form flaws fixed by finding the right rotation.
Continue to work on getting better:
Use the fins and snorkel to continue to develop your kick. It should come from the hips and not the knees. Use the arms down and thumbs into your glutes to make sure you are kicking from the right place. You should feel your glute tighten and relax if you are kicking from the hips. You will never feel them tighten if you are kicking from the knees. Your kicking should be small and compact with a higher tempo. No big slow kicks.
Feel the rotation coming from your hips. Also remember your hips and shoulders move together in swimming. We want to have quick powerful rotations to develop speed in the water.
Wall kicks 5x:45 w/ :15 rest
-Kicking with buoy - to develop a tight kick
-Kicking arms out front
-Kicking arms down by side thumbs in glutes - make sure you are kicking from the hips
-Kicking on back - helps to develop the up stroke of your kick
-Kicking on side - over exaggerating the rotation
-Kicking alt from front to back - feeling the kick while rotating
-Rotation kick - this is where your arms are down and you snap those hips as fast as possible
-Single kick w/ pull - linking the kick with the pull across the body-6kick switch - kick on your side for 6 then take 3 strokes so you end on the opposite side kick for 6 then repeat