Just as with an oak barrel, you get diminishing flavor with each usage. If on a small barrel you age for 3 weekson your first usage, you may have to go 3x that on the second usage to get the same flavor. And not much at all after that.
With oak cubes, I use them once for regular beers or wines. And then store them in my freezer labeled with what they were used with. They work really well for sour batches where you don't want as much oak flavor, don't care as much about sanitation, and where you might want to split a batch to pick up some subtelties of a spicy red wine, malty barleywine, RIS, etc.