Mostly as an investment, Collecting them and waiting for a price improvement to earn profit both on daytrading "for usd daily value" and as well as a long term investment to accumulate some btc on long term value.
the same for me to be honest, bitcoins are just an investment for me and that is why i hold it
Most of the people are buying bitcoins just for holding it and count me in with that. For I have bought bitcoins when the price is still $500 and somehow as of now I did got some profit already but still I am going to keep on buying if I can consider the price is still low. But there are also people who are buying bitcoins just to gamble and to trade.
Buying it for trading is an good choice as you will be able to multiply your coins in long run with trading, and trading bitcoins is always best in compare to simply holding them where you cannot make regular profits.