It depends on what you want out of your cigar. An Opus X will become milder with time, but is that what you want? The Petite Lancero is in your face young, but three years down the road, it has been tamed. Not necessarily a bad thing, but not what its producers tout it for. I "lost" a box of Avo #1s because I tried to age them years ago.
I believe age helps balance a cigar. By this, I mean it evens things out between the wrapper, the binder and the filler. It marries the qualities of these individual parts together. You get a better burning cigar with a better balance between the pieces. Think about humidy alone -- can a cigar, sitting in a closed box for a month, achieve equilibrium throughout its parts? IMVHO, I don't believe so.
As for Cubans, I like them aged. The difference between a RyJ Robusto El at delivery a couple of years ago versus today is indescribable. The cab of Partagas Lusitanias I have only gets better with age. I try (not always with great sccess) to age my cigars (Cubans).
Aging NCs? It doesn't hurt to try. Smoke one every month or so to get a feel for the cigar. If you like it, then smoke 'em like there's no tomorrow. Cubans? Let them sit. Trust me, it's worth the wait.