So I tried this for a few months last year. Although I didn’t rinse 15 mins afterwards or anything - I just spit as much of the toothpaste out as I could.

Couldn’t really tell a difference other than it was strange feeling to have all the toothpaste remnants in your mouth. Maybe my teeth were slightly whiter? I eventually went back to my old ways of rinsing. Maybe I’ll try it again though.