What is the purpose of close fist swim drills?

Helps you properly use your forearm in the catch phase (feel the water on the forearm) and have the optimum elbow bend through the stroke.  But a biggie is to also concentrate on body position/rotation with the closed fist stroke to really have the forward propulsion.

That is the purpose--proper use of the forearm as part of the "paddle" that you anchor into the water and use to move your body forward. The underside of the forearm is where you want to feel the pressure of the water on, and the underside of the forearm should be facing the back (think parallel with the back wall of the pool) for as much of the underwater part of the stroke as possible.

Think if you were hanging off a flat roof, trying to pull yourself up on it. Would it be easier if it were just your hands that were on the roof, or if your entire hands + forearms were already on the roof? Similar motion in swimming. It's going to be a lot easier and more effective if you can pull your body forward using your whole hand and forearm (and if you use your core strength to anchor your arms firmly on the roof and pull yourself up, instead of just using your arm strength).

My experience as a coach, and this is also the opinion of Swim Smooth (one of the major swimming resources for triathletes / open water swimmers), is that for the purposes of more effectively using the whole arm along with core (instead of just pulling with the hands), there are better ways to do the traditional closed-fist drill. My personal preference is to do it with a loose hand / straight wrist. This accomplishes the same purpose without these drawbacks of a fist:

- fist tends to make people c.o.c.k. their wrist at an angle; loose hand keeps back of hand/wrist/forearm in a nice straight line.

- fist tends to make people clench their hands (creating tension/stiffness all the way into the shoulder and even chest/back) and pull/fight their way through the water instead of relaxing and sharing the work through engaging the whole arm/torso to move through the water.

- loose hands still allow the fingertips and hand to "feel" and initiate the catch (beginning of in-water part of stroke)--which is exactly what they are supposed to do--but still removes them from pull effectiveness in order to focus on forearm (and upper arm).