Yes, as betta_newbie22 said, the gravel really is mostly for your enjoyment. Unless you have a planted tank, of course, but then you might end up using something other than gravel.
Gravel can, in an established and cycled tank, provide a home for beneficial bacteria. It makes a great buffer if you have to get a new filter because one died or something like that because it re-cultures the new filter much faster and you are less likely to have to completely re-cycle the tank.
So in short, gravel is nice to have, but not necessary.