No travel site has saved me as much money as Airbnb–the 10 rooms and the two apartments I’ve booked through the site represent thousands of extra dollars I didn’t have to spend on overpriced hotels at events like Mobile World Congress and Google I/O. But no other travel site has left me thinking so much about its effects on the places I visit.

The vision that Airbnb sells, and the reality I’ve seen in half of those 12 stays, is somebody renting out a room or (when they’re traveling) their entire residence to make extra money on the side. I always appreciate the effort these hosts put in–the labels on everything, the well-placed power strips that hotels often forget, the advice about places to eat and drink nearby–and I like the thought that I’m helping people stay in their homes or apartments.

(A friend in Brooklyn has rented out the extra room in his apartment for years; seeing him favorably review an Airbnb room in Denver put me at ease with staying there for last year’s Online News Association conference.)

But Airbnb also features many other hosts who list multiple properties and, in some cases, have purchased many or all of the apartments in a building to rent out to budget-minded travelers like me. In the latter case–like the room in San Francisco I rented this week that appeared to have once been a single-room-occupancy apartment–you can easily imagine that without an Airbnb, people who live near those places would have more housing options.

That concern, sometimes pushed by the hotel industry, has led many cities to try to restrict Airbnb. In Barcelona, that crackdown meant the apartment in the Gothic Quarter that I’d stayed at for three years in a row was off the market this February because the host couldn’t get the required tourist license (I found another apartment that did have it, or at least said it did). In San Francisco, it’s led the company to start collecting occupancy taxes (which is fine with me).

I don’t want to overstate Airbnb’s effect on a housing market–certainly not in the Bay Area, where development policies founded on delusional entitlement have done far more to jack up residential costs. But I do worry about this.

And then I continue to book on Airbnb when crashing with friends isn’t an option. When the alternative is eating $200 or $300 a night on a hotel room or staying in distant suburbs, what else do you expect me to do?