It's almost funny that the city is engaging in rent-seeking behavior against renters. In this move San Francisco makes it clear that they believe they own your property and you merely occupy it on their whim.
Some people rent out a spare room now and again for extra cash, and some people have multiple properties that are occupied exclusively by Airbnb renters, essentially running an unlicensed hotel.
The latter can be extremely obnoxious if its your upstairs neighbor, not to mention the effects that being discovered by Airbnb real estate investors can have on a town or neighborhood.
In this move, San Franciso makes it clear that you can't change the use of a property without permission.
Living in a city is a big trade-off. More jobs, less liberty.