Sealed bottles last long enough.
Once opened, they loose their zip.
Those last few pops of a long-lived shelf queen taste nasty.
Any Bartender worth his Spirits will agree.
Buy volumes that fit your consumption.
Pints, Fiths etc for you teetotalers.
I have a half full half gallon of Vodka in my shed. I use it to clean grease off of tools, and when my wife tees off on me... It does a good job tempering foul moods.