What do you use a simple fixed pulley for?

To lift things up more easily. Duh.

You see, if you get more and more pulleys and keep putting them on the same rope, your load would become easier to lift as you added more. In fact, if you had a rope that was strong enough, one could easily lift a Black Rhino using 4,993,374 pulleys. This is just a theory, however. There is no one rope strong enough to lift that. And, nobody will ever try to do that. We have elevators for a reason, folks.

The elevator pretty much ruined the use of a pulley.

Another thing you could use the pulley for is to make a movie set that is set in a place in which you would need pulleys. For example: a place without elevators or pistons and a lot of heavy rhinos that need lifting.

One last use for the pulley is to hang it up in an elevator as a symbol of uselessness. It can be used to make a statement. The statement may vary depending on where the elevator is located, the weight limit of the elevator, etc. One good way to be very ironic is to take 4,993,374 pulleys (the amount it takes to lift a rhino), hang them all up in the elevator with rope and everything, and make sure that the weight limit of the elevator is under 2,500 lbs. If you live in an industrial area, you are out of luck. This works best in an elevator that is used by lots of people daily, but is in grave need of an upgrade.

In short, use your pulley to lift heavy things. Like rhinos.