You spin your money.
You may spin some of them in bitcoin. What if you start spinning other people's money in bitcoin for them (and have a cut)?
Practically that mean that you need to become not just bitcoin wielder, but also an exchange and a seller.
Lowering abstraction one step more - your smartphone BTC wallet app should allow you not just pay and receive, but also exchange for fiat and buy stuff for someone else (could be tricky).
One could say that you already can do that in programms A, B and C and I'd agree.
It is just making it as a one app (or webservice?) makes a killer feature IMHO.