Photo by the very talented Erik Johansson. See more at http://www.alltelleringet.com/
Break a lot of bad pots.
My rule is, if it offends me, I break it.
If the piece glued itself to the floor of the kiln and I had to break it off, definitely break it and stick it into the bottom of a flower pot.
If the piece has a crack, a break, a dangerous glaze result and doesn't contribute to the "look", break it.
If the structure or the glaze just didn't work, break it.
BUT
If the piece was a good idea gone bad, keep it.
Photograph it.
Analyze it.
Try it again.
Or pack it away and forget it for a while.
I have to admit that there have been a few pieces I've applied the hammer to that I wish now I hadn't been so hasty. Or so persnickety. That was when I first started making ceramics and had this image of perfection embedded in my mind. After I went to a few NCECAs and looked carefully at a huge variation in other people's works, I edited my ideas of what is and isn't perfection.
I do have a series of mugs that I thought would be a good 'family' with variations in shape, but uniform in glaze and unique (same) handles. I still think it's a good idea, just didn't pan out that time. They are sitting on a shelf in the studio as a reminder.
So, trash the 'failure', don't trash the idea.
P.S. Don't forget your goggles while you're happily smashing stuff!