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.
one of a most common reason of peoples buying bitcoins. they buy bitcoin to earn some extra price when the price increase.. because bitcoin is a very valatile currency and price increase and drop so often so it is always profitable to buy bitcoin and sell them when the price increase no matter if price increase very little bit or increase too much.