I think this depends on the size of the startup. If you've only got ~10 employees, decent office space, furtniture, catering, etc. in SF or SV could be a meaningful fraction of your overall expenditure. The more employees you have, though, the smaller that fraction is likely to be. Even so, I think you're right - downgrading your office space would get you maybe a couple months of extra runway, vs. reducing salaries or staff, which would get you a lot more.