They're pretty great for reducing the volume of your waste for those of us who care about such things. Supposedly they can also help increase the longevity of your pipes by reducing gunk buildup. And when I lived in a tiny apartment, it was pretty nice for getting rid of smellier foods instead of letting them sit in the trashcan or having to haul it out to the dumpster.
I lived a long time without one and wouldn't say they're a necessity or a big game changer or anything. But it's a pretty nice convenience.
Easiest strategy ever to implement.