ranjit far more useful for memory than technique
I was just thinking this same thing, that Ranjit is talking about technique but many people are thinking about learning the notes.
As discussed, slow play is absolutely relevant for pianists of any level, really of all levels.
But how does one develop the ability to do an extended trill? Or to play a rumbling bass line that takes requires you to send your LH down a cascading line for four-notes chords in a finger twisting progression at a punishing tempo?
There are probably other examples, but these things require movements that are physically different from what you would do if the music were slow.
Having said that, speed before one is ready for it just leads to sloppiness… so it’s a fine line, I imagine.