All you can do with them is trade them.
But at the point where you want to put them for good use and buy something, you have to convert them either into fiat, or bitcoin.
And that's the point why I think the alt ralley helps bitcoin too.
A good part of the alts will end up to be bitcoin sooner or later.
good point. jimmy song has written a nice blog post concerning this:
https://medium.com/@jimmysong/why-the-bitcoin-dominance-index-is-deceiving-80ae324ee2ac
If that last section was too confusing, consider this thought experiment. Suppose I make a new coin tomorrow called FoolCoin. I premine the whole thing (100,000,000 coins) and only make 10 coins available. Perhaps I create a marketing campaign and even get enough people to desire the coin that Poloniex lists it. I sell just 1 of the coins for $10. FoolCoin now has a $1 Billion market cap. The next coin, I sell for $11 and now FoolCoin has a $1.1 Billion market cap. If there’s enough demand, I eventually end up selling the other 8 coins for $20 each at which point, FoolCoin now has a $2 Billion market cap.
I’ve just added $2 Billion dollars to the cryptocurrency market cap and have reduced Bitcoin dominance by a few percentage points. But did I really take anything out of bitcoin other than perhaps a few hundred dollars worth?