"it'll fill up relatively easy (compared to the market it is in) so you'll often have relatively low vacancy (but even one month empty is paid for by ten months

"it'll fill up relatively easy (compared to the market it is in) so you'll often have relatively low vacancy (but even one month empty is paid for by ten months rented." You are assuming that the marginal cost of turnover is zero, which it definitely isn't. Putting a unit on the market, showing it to prospective tenants, processing applications, background checks, income verification, etc is labor intensive and expensive. This is during the period where you have 0 income from the unit.