Always - after rinsing my reels with fresh water when I first get back home.
Once a week (or more if need be, depending on how hard I'm hitting it) I wash out the spool with warm soapy water to get the salt out, or if they're pretty salty remove the washers, wash and dry the fiber washers and polish the SS washers with Formula 2001 - which has urethane in it - and then reassemble -
Keeps the drag nice and smooth on the old Penns.

-
Straightened out a 4/0 VMC on a nice fish by not keeping an eye on my drag washer crudded up with salt

and
that ain't gonna happen again.