I don’t floss every day but I do floss and frequently dislodge food caught between teeth or whatever. No one will convince me that leaving it to rot inside my gums and teeth is good. At the very minimum, it’ll stink.

I also occasionally develop a minor infection in my gums if I’ve not flossed in a while that flossing the area relieves. As a sample of one, it’s effective. If I do it it relieves the infection, if I don’t it doesn’t. Maybe my experiences don’t generalize but I suspect I’m not that rare of a human being. I generally have healthy teeth and gums, never have had cavities, and my dentist says she’s rarely seen healthier teeth especially at around 50. YMMV.