Assuming we're talking about smash attacks, with the A button plus left or right direction, Ness moves a bit further. Here are a few and if it's safe to say, useful things to use the C-stick for.
Mr. Game & Watch
Pump:
Because f-smash in general moves Ness a bit further towards his opponent, Ness would once again get hit by Mr. Game & Watch's neutral A. If you use the C-stick, Ness does not move slightly. In fact, he doesn't move towards the Pump at all. His f-smash would land a perfect tipper on Mr. Game & Watch. Can this really work? Well, landing an f-smash three times in a four stock match against Mr. Game & Watch says yes.
Manhole:
It's the same method as before and can work. This is in no way to bash Mr. Game & Watch or the players who main him but just useful advice of how useful the C-stick can be.
Pivot Smashing
Either way works. I prefer pivot smashing with the A button instead of the C-stick because you move a bit from your opponent but still have that slight movement to land your f-smash close enough and possibly tipper. The C-stick makes this method a bit easier, though. Does this actually work in a match? On rare occassions, yes. I've done it on three different opponents. One on BadGuy's Bowser, the other on Durango's DK and the last one on _clinton's Yoshi. </braggingrights>