You can do this but I think its sometimes also not worth it to do it with debit cards because some are charging very high fee's if you ask me.
But it wont be that easy to earn some money with Bitcoin because it will also takes a long time until you can make profit.
If you spend the bitcoin and then buy it back, it is good for the circulation of the bitcoin, it will make the price rise.
I spend my bitcoin by paying my bills then after i work again for bitcoin to earn more and save that is the cycle of my bitcoin
Indeed the most of people spend their bitcoin to complete their necessary such us pay a bill and buy some good, but not seldom people who spend their bitcoin in real life but before it they change bitcoin into their own currency . It is what commonly people do to spend. And i agree about spend bitcoin and then buy bitcoin again can make good affect for life of bitcoin.