Ever found it so annoying when you've had 3 friends round your house, and you all want to play on the console? Ok, so you have 4 controllers... excellent... but oh no! The console is next to the TV, and the only power socket is at full stretch to have it there - it has to stay in that position, next to the TV.
Now this in itself isn't a problem, however, when the only chair which can be moved nearer the TV is one seated, and is the one you usually use for single player, then your friends need to sit very uncomfortably near the TV, on the floor, being at a distinct disadvantage in-game. Game controller leads aren't that long, and if they can't reach the sofa where your friends want to sit then that's not great it is? Cordless controllers fix this problem.
Oh yeah, and also think about how many times you've had to untangle them/tripped over them/knocked over drinks with them, etc. These are just a few examples i can come up with. Wireless mice are pretty pointless, i admit - and the ones i've come across break a lot, but wireless console controllers are very very useful, in my opinion.