That saying came from when people used to butcher their own hogs and use everything "but the squeal." Pigs ears, stomachs and feet even found uses. (Can you imagine blowing up a pig's stomach to play kickball?)
I was thinking of this today as I cut up some apples that were getting soft for apple sauce. The peels and core could have been used for apple jelly or syrup or to make pectin for other jellies or jams. There could have been nothing left "but the squeal," and since apples don't squeal (at least I've never heard one), there would have been nothing left but the pulp from which the jelly was strained. I suppose I could have salvaged a few seeds and planted them, too.
That's not extremely frugal. That's not being wasteful. Sadly, we live in such a wasteful time that not wasting things is thought to be strange or weird.