All boats used to have enclosed cockpits with a fixed transom. Most boats had a bridge
deck in front of the
companionway to prevent flooding down below if pooped. If they didn't have a bridge
deck, it was de riquer to fit the
hatch boards at least part of the way up to prevent flooding in susceptible conditions.
Racing boats initially went to the open at the rear cockpits possibly to save weight in the '80s, IIRC.. They offer a no restriction way to drain the
cockpit but I always fear stuff going out the back whether by wave action or it just happens.
So, no it's no big deal to have the
cockpit closed off if you have a bridge deck or put the
hatch boards in threatening conditions.