TheBoringPianist
I think there's definitely something to spaced repetition for pieces once they've reached a certain level. I've also found it helpful for keeping old repertoire reasonably fresh while digging into something new.
That being said, for initial learning I still think concentrated practice across multiple days is the way to go. I've had to practice the Franck-Bauer Prélude, Fugue et Variation every day for the past 2 weeks just to reach the point where I'm able to play through without excessive slowing down, and I don't think breaking up those 2 weeks would have helped much. Now that I've reached this point, though, I feel like maybe introducing some spacing could help.
It may be worth noting that while not a direct comparison, the fastest you can get a private pilot's license (both by # of flight hours and calendar time elapsed) is to do it all in one go over the course of a week. This is because on a weekly/biweekly flight schedule that fits more people's work schedules you lose too much over the course of the week and have to spend extra time refreshing your memory. Is it possible that adding some spacing after the first few days would be even more efficient? Maybe. But most of us need to work heh.
Honestly, at the end of the day, I feel like the effect of a single good night's sleep (0 to 1) is far more impactful than the effect of e.g. 1 night vs. 2 nights vs. 7 nights. So I think I should just sleep more heh