Freezing food for later consumption is a good way to stretch your grocery bill but, for the best-tasting, safest leftovers, you only want to freeze and thaw cooked food once.
Photo by Lisa Clarke.
According to Bon Appetit (which has a bunch of great tips for safe freezing and thawing in the link below), the reason is two-fold. In terms of taste, repeated freezing and thawing can turn your meal into mush. Due to the nature of dihydrogen monoxide -- which is one weird molecule -- water actually expands as it freezes, which can rupture the cell walls of your meat and vegetables, making them unappealingly mushy.
In terms of food safety, each thawing introduces new bacteria into the mix. Though freezing can halt bacterial growth, it won't necessarily kill every single type of pathogen introduced, so it's best to limit your number of thawings. (Honestly though, my main concern would be taste and texture; mushy food is extremely unappealing.)
How Many Times Can You Actually Thaw and Refreeze Food? [Bon Appetit]