Opening cereal/fruit/granola bars and similar foil wrappers. I would tear them on the serrated part and then only a sliver of the wrapper would come off and I'd have to try to widen the resulting hole in order to extract the bar, often crumbling part of it in the process. However, quite by accident I discovered that if I instead ignore the serration and tear against that foldy seam part that runs down the entire bar, then it separates right down the middle like magic and I can easily remove the bar. Often works on 8/16oz cheese too.