I remember what a revelation this was when I first heard it, a practical shorthand for communicating that I didn't want scalding water up to the very brim of the paper cup.
Today, of course, I was not in a coffee shop but in my own house, but I have learned the hard way that when the cup is full the carpet bears the brunt of it. So "leaving room" is now a mantra both at home and away.
It's not one that comes easily to me, however. I'm an up-to-the-brim kind of person, and restraining myself enough to leave room is an act of restraint I'm not always willing to make.
The little bit of wisdom that flew down on me when I glanced at my not-quite-full-cup this morning was that it's an easier way to live and is perhaps worth a more-than-occasional try. Living "with room" means not packing every day quite as full, leaving minutes at the beginning and end to think, ponder or meditate. Living "with room" takes some of the edge off he day.
(My brother is an excellent packer, but even he left room in this well-stocked box of gifts.)