Unfortunately there is not much point to applying a fisheye effect digitally unless you happen to like the specific effect that a digital fisheye filter has. For example, it can sort of simulate the effect of looking through a glass ball.
Actual fisheye lenses exist because they can get a very wide angle of view, and don't need to worry about keeping straight lines straight (ie being rectilinear). This reduces cost and size of the lens greatly, but with the obvious caveat that the image is highly distorted - straight lines become curved towards the edge of the image. It also makes it possible to do something that isn't possible if you're keeping to rectilinear projection, and that is to extend beyond a 180 degree field of view. You can imagine that there are some practical uses for this, when you want to show a wide field of view and the distortion doesn't matter.
When you do a fisheye effect digitally, you do not benefit from any enhanced angle of view. You are only emulating the distortion.