The most common use of bitcoin would be trading and buying goods,
thousands of people worldwide trade bitcoin each day for other altcoins or even fiat money.
bitcoin trade over 2M daily on the coinmarketcap calendar:
https://coinmarketcap.com/currencies/bitcoin/In fact bitcoin is not created for trading and investment, but unfortunately still the facilities of bitcoin to use it as currency is not available every where and therefore we are using it for trading and other such purposes. i think in future we can expect to use bitcoin as currency in stores both for online as well as for offline purposes but it is in fact depending on the number of bitcoin users. As soon as the number of bitcoin users will increase more opportunities will he people to use bitcoin as currency.