This feels sensational. Imagine a common scenario: a unit is rented for 2 years (24 months), and then is vacant for 1 month while the owner repaints, performs maintenance, and relists the property for rental. That is 1/(24+1) = 4% vacancy. Given you can easily get to 4% vacancy with simple turnover, you can see why very low vacancy rates are bad for renters: they indicate it is extremely competitive to find housing. You can see this anecdotally in extremely tight housing markets like NYC where renters looking for apartments often report they need to move extremely quickly to secure rentals and some people even ofter to pay more than the listing price for desirable apartments.