Well it depends on your personal playstyle, but the advantages a controller has over a keyboard are as follows:
- 360 degree movement (as opposed to 8 directions of movement)
- More precise ability to pick your speed etc. (You can move really slow, or really fast depending on how far you push the stick, with a keyboard it's either fast or off).
- Access to more buttons without stretching your fingers all over the place
- Easier access to certain moves which default to the right stick on controllers (like one touch controls in FIFA, or the Hit stick in Madden)
Really, I use a gamepad in pretty much every type of game except 1st person shooters and some third person shooters, because you're generally sacrificing precision (mouse being more precise than the control stick, keyboard is less precise than the control stick) for convenience, and you don't need much precision except in shooters.