I think a good way to see the difference is to find a ball that perfectly matches with a pattern, then take a ball in either direction. Both balls will get you to the pocket, but one will outcarry the other by a pretty big margin.
For instance, last week in league I was throwing my Erase-it. I was getting to the pocket, but that ball was a little too strong by the middle of the second game. No matter how deep i moved, I couldn't get the ball to carry, it kept rolling too early. So I step back and pull out my Thing Returns and I carried the next 4, where the previous shots were either weak 10's, or some other single pin spare.
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The clock on the wall says 3 O'Clock...last call...for Alcohol!
"I love a martini -- but two at the most. Three I’m under the table; Four, I’m under the host." Dorothy Parker