This is pretty helpful though...
www.boardcave.com.au/the-surfers-corner/surfboard-finishes-hot-coat-or-gloss/Excerpt:
"A Gloss Coat is yet another layer of resin applied to the board after a hotcoat is applied and sanded down. It is another form of resin also with a wax solution added to give you and extra layer of protection and well as an aesthetically pleasing look.
Gloss Coats are usually found on longboards, alternative surfboards, or retro style of boards. It does add weight to a board, so that is why the majority (not all) of shortboards do not get a gloss coat.
That added weight can come in handy for longboards and some of the retro style boards.helping to keep momentum going down the line, etc. and the extra resin gives and added layer of protection against any dings your board my be prone to. It does cost a little extra to add a gloss coat, but if you care about the longevity of your board, it is a small price to pay.
Remember, there are two ways you can ask for your gloss coat. Sanded or polished.Sanded GlossA sanded gloss coat is exactly what it sounds like. The Gloss is laid, dries, and gets sanded to a high grit. A polish is the same process but when it comes to sanding, it is usually wet sanded and then polished to give you a nice mirror like glossy finish.
Some people claim that a sanded gloss is a little faster than a polished gloss due to the slight texture of the finish holding on to a very small layer of water forming a barrier around the board. That small layer/barrier stays with the board allowing friction-less water against water glide."