You might say "I finished my game", "It was just a test game", "the art was so terrible, I'll never use it again"... but you never know when you'll need them.
I discovered "no programming game making" two years ago and made this test game(BounceFighters in case you want to check it out), it was for pc, kind of a cross-over between pong and street fighter (as crazy as it sounds)and just today decided to re-make it HTML5 with the powerful features of Construct 2, but after one hour I gave up to the idea that my files were gone.
Too lazy to do the design again, I said goodbye to my remake.
So again, for all of you that have just finished a game... BACK UP!! BACK UP!! BACK UP!!!