Depends on the strength of the brew itself and what flavors you are going for. Lightly hopped, light malt beers will diminish after time, but will still be drinkable.
High OG beers hold flavor well but the hop profile slowly gives way to the malt flavor.
For example, I had an Irish Red that I hopped above style, and it was well balanced hop/malt profile. I "lost" a 6 pack of it in the cellar and when I found it a year or so later, the hop profile had faded and it turned into a heavier malt flavor that I remember.
Aging is very important for some styles, and a few will not taste "good" if they are still green. Usually, the higher OG or the higher the ABV, the longer you may want to condition.