Who made the rule that there is only room for ONE cryptocurrency? The market will decide that. There are lots of interesting ways for a lesser and greater cryptocurrency to complement one another.
Actually, no, there really isn't. Any reason I've ever been given that any other coin can "complement" BTC has been weak at best and amounts to "because I want to print my own money still *boohoo*". The only possible goal of LTC, as I've said before, is to ruin the idea of cryptocurrencies in general. There have been lots of people who have been turned off from BTC simply because LTC and other alt-coins exist.
"Why waste time on money on BTC if people could just jump over to the exact same thing with a different name and leave me broke? Sounds like a scam" Hence: scamcoin
Now, the market WILL decide. It'll decide that you're a victim of a pump-dump scam and you've just wasted your time. I'm just trying to help you out and tell you that you could be doing something productive with BTC instead of being an emo-kid that's upset you can't print your own money.