I think the biggest danger is for the owner of the tank dosing like, one for me, one for the tank ;-) But joking aside, this method sure does work but requires fine tuning over time. How it works was explained already, but there are maybe 2 things to mention. First, if you plan dosing vodka or any other carbon source like vinegar, sugar, you need a skimmer which is capeable to skim out the increased amount of bacteria. Best is to have a skimmer bit oversized for your tank. Another good thing is to run your skimmer with ozon so you always have a good oxygen level in the water. Overdosing with vodka can lead to a bacteria bloom very very fast which will reduce the oxygen level in the water very fast!
With all stuff you dose into your tanks, always start low and slowly increase the level.