Depends where the damage is - you might find that it starts shrieking when you get up to speed. While I have heard it argued that the high frequency shriek of a damaged fin acts as a shark and whale deterrent, I find it annoying (much the same as the marine life does I guess!

).
It's usually pretty easy to fix - make sure you use epoxy NOT polyester or it won't stick properly

- 15 minute araldite etc. is okay, and then wet sand it back with some 280grit paper on a hard block to get the shape right.
Packaging tape works well for masking as the epoxy doesn't stick to it - I've had a bit of success taping the most damaged side, then holding the fin flat with the taped side down, and letting the epoxy run down into the damaged area, building it up a bit around the leading edge.
It's never going to look quite as pretty as it used to, but that's to be expected when the rocks sneak up and give it a hiding.