They can (almost?) always just be inferred, I think (it's been a couple of years since I programmed in ocaml daily).
I personally like using them anyway. If you've done something wrong I recall the parser can sometimes give better error messages if it has them around to orient itself. And for all the complaints people seem to have you really can grow to like them aesthetically - there's something pleasantly blocky and definitive about them I find, like the satisfying thock of a good keyboard.