As a 10-year San Francisco resident (and my husband has lived here for 20 years), I'll reiterate what others have said, most of which comes down to: exercise caution. I say this as a former renter and as a former accidental landlord who rented her place in Chicago when she couldn't sell it during the housing crash. I lived both lives for many years. With that out of the way...
Even in non-rent controlled units, tenant protections in San Francisco are ridiculous in practice. They ensure we will never rent our house.
After 30 days, a "hotel guest" becomes an official "tenant" in San Francisco, with all the protections thereof, lease or no lease. If you choose an AirBNB type situation, for example, and that guest stays for 31 days, look out, you may have a squatter on your hands. There is a housing shortage, and I know of at least one situation in which a tenant did this on purpose for exactly this reason. It then took the owner a LOT of money and legal battle to get the "tenant" out. If you stay under that limit, you should be fine.
There's a lot of money to be made in temporary rentals with less grief, I believe. You also may be able to get on a list of companies like Google and others who need temporary housing for visiting employees and interns.
It is virtually impossible to quickly evict a tenant in SF, even for very eviction-worthy things like failure to pay rent. We have friends whose tenants did not pay rent for over a year and it took another full year (that's two years of rent-free living for the tenants) to evict them, also after great legal expense and pain. No one cared that our friends (who lived in the same building as the non-payers on another floor) nearly lost their house and could barely pay the mortgage without the rent from the other unit. The law only cared about the tenants. The lease amounted to almost nothing in this case, though it was a CA standard lease that they'd paid a lawyer to review.
All of this nonsense is, of course, and part of why AirBNB and VRBO are so attractive, but also why AirBNB is bearing the brunt of the blame, as we see in measures like Proposal F on the Nov. ballot.
All a long way of saying: If you decide to rent to a long-term, traditional tenant, be prepared for an expensive, drawn out legal process, costs, and all that. Make sure you are *very* secure in the $900/month room rental situation because, should you need to get back into your condo, you may not be able to do it quickly. Theoretically, it's easy for the owner to move back in, but in practice it's often not. I have a horror story about that as well, neighbors who wanted to move upstairs to a renter-occupied unit so that they could move elderly parents in downstairs. That took more than a year and tons of legal drama and fees.