If you want to make a noticable profit from Bitcoin mining nowadays you'll need to use ASICs. Litcoin (and many other altcoins) can't currently be mined using ASICs or even FPGAs, but can be mined using GPUs, so the purpose is mainly to give formerly BTC-mining GPU rigs something to do. Most altcoins can be exchanged for BTC or fiat. Eventually LTC will be as common as BTC is now, it's just that Bitcoin had a head start.