This is proven by neuroscience. Spaced repetition.
I'd have thought repetition was more about retention than the described "learn one new thing every day".
I'm also curious what new means here. Is attempting to research and retain (eg SR) some small fact the goal? Or would it be learning novel modals, such as new skills or new ways of thinking - which i imagine would be quite difficult in a day of course, just thinking out loud.
For SR to apply i imagine it depends on the underlying set of SR cards/etc. If you're just topping off on well known material then SR can't do much - but if it's well known material, there's often not even a review stage to have - all the material won't be flagged for review.
However if you have several items that you're reviewing then the SR algo has determined you don't know it (or perhaps they're new, but that's a bit besides the point).