Depends what you are doing with it.
We once had a property empty for well over a year. We bought it cheap but had two other properties in the pipeline to be worked on so didnt get round to it. (Had other jobs to do too).
Some Landlords over value their properties rental worth, we always opted for filling it up so dropped the price accordingly. However our properties tended not to be rented for long so it was ok, if you are on for a long punt then this option is not so good hence landords hanging on for best price.