Crisps, and other cooked fruit recipes, are a great way to use up fruit that is still good, but past its prime for other uses. I had a pound of strawberries that made their way to the back of my fridge that had frozen and re-thawed into mush. So I pulled a bag of plain, frozen rhubarb out of my freezer, chopped up the mushy strawberries, and mixed up this filling. It's bagged up in a freezer ziplock and ready to pull out another day to defrost when I want to make dessert but don't have the time or energy to pull it together.
Avoid the hassle of making individual batches of topping: increase the recipe in whatever multiples you would like (x2, x4, etc), divide into labeled ziplock bags and store in the fridge (1 month) or freezer (3+ months). Whenever you make any kind of fruit crisp, grab a defrosted bag out of the fridge and crumble over your filling.