Second, as a disposable, dead layer, it also provides protection against UV light and such. We don’t think of living out of water under the direct radiation from the sun as being particularly difficult or the environment harsh, because we casually do it every day, but it was a very hard problem for life to solve.
Oh yeah, that's a good point! I'd typically be more concerned with the drying out part for a lot of aquatic life, forgetting about the UV exposure issues.