It can happen almost anywhere, you want to transfer something from a computer to your phone or vice versa.
You have your phone and also an USB-cable but you’re not at your PC where all drivers are installed you are on the go (maybe university or at a friend?).
Maybe you are not even able to install drivers as you don’t have the necessary rights on the system?
How can you connect your phones memory to an unknown PC that supports USB-Sticks?