For times when you do fly over water. The PAR at NPA is used regularly and it sends you out a ways. Also for trips to the Keys, like I mentioned.
When I was wearing LPUs and life rafts, I wasn't in a CNATRA bird, so there were other considerations.
People always try to sea-lawyer their way into a dry vest. Honestly, whenever I had a syllabus flight, on my INAV/VNAV solo, and whenever I observed solos, if we went to Panama city, I wore a wet vest.
I had solo studs go "well, we'll be flying along the shoreline of the East bay, so TEEECHNICALLY we're over land". I politely suggested wet vests.
My justification is that I'd rather be a little more uncomfortable with the LPU in the cockpit and not need it, than to be a bit more comfortable with a lighter vest and then be floating in the East Bay or in the Gulf wishing I'd had my LPU as I'm treading water. Sometimes it's VERY clear when you step back and realize what you're arguing about.