Leaving any cooked dish such as a casserole, spaghetti bolognese, lasagne or what ever allows the meat and the other ingredients to basically marinade in the stock/gravy which the dish contains. It also helps with further tenderisation of any meat. The only meat which is cooked in a sauce and which I personally don't leave at least overnight before reheating and serving are pork dishes.
Curries are also better if they are held cool overnight. The spices tend to be enhanced. I suppose Chilli could be loosely classed as curry type - or not depending on your opinion. Don't leave boiled rice overnight - it is easily attacked by a fungus which will make you awfully ill - I know this from experience.
Cooked Rice - Rushcliffe Borough Council