1" sideseam solar SPEEDO

[Byron]

1. Better body definition (and can let you swim faster according to some - but better make sure the fit is good as loss of shape in some materials can make it a mistake)

2. Swimmers might do that in training for a drag effect and so make them work harder on their lap times. Less so now but formerly common practise in water polo as a defence against aggressive underwater grab and pull tactics.
(somewhere on the www is a pic of a water polo international emerging from the pool with no bum cheek cover left on his speedo!)