It's mostly console games that get ported (badly) that will make you feel the need for a joystick because they port the keys 1:1 and in a lot of console games trigger buttons are shift keys (exactly because the controllers have less keys than needed) and don't allow you to bind stuff directly. So instead of binding, say, '2' to an action you can only use that action with a shift key (e.g. R2 on the controller) plus another key. While it's easy on the controller, this can cause issues mapping to a keyboard because of the finger gymnastics.

Another issue will be with any game that relies on both analog sticks to be used as, well, analog. A racing game for example with throttle and wheel control will suffer on a keyboard/mouse scenario.

I personally have two gamepads (g13 for MMOs, orbweaver for FPS) and a steam joystick for games that are better played on a joystick. Ignore all this elitist BS and play with what you want. Just know you'll be in severe disavantage in any multiplayer shooters if you don't use mouse for aiming.