As a former national-level swimmer, I always shaved my legs/arms and tapered my training for a big meet twice a year. I found that combination to lower my time

As a former national-level swimmer, I always shaved my legs/arms and tapered my training for a big meet twice a year. I found that combination to lower my times by about 1 second per 50m, or about 5%. I don't know how much of that is attributable to the shaving, but I will say it helped me "feel" way faster.