I'm not the person you're replying to but if you actually wanted to live by yourself in SF you could easily spend anywhere between $3500-5000 on rent. Even at a $175k salary that's more or less half of your post-tax pay monthly. For sure that's still livable, but may not make financial sense. Staying with a few housemates take that monthly cost down to $1500-2000 which allows for much more savings, so eventually you could buy a house (maybe somewhere else outside of the bay!). 9 housemates is a bit extreme though.