This isn't rocket science, and it is something professionals are taught to do.

But I'm also not trying to play extremely fast. If my goal was recital rather than composition, I would use it more. My recordings[1] are mostly total improv, free jazz, with a vocals track (later deleted) that states what chord changes are coming up, and then improvise over the first instrumental track while listening to the chord announcements.

https://soundcloud.com/jeffrey-benjamin-brown

All the exercises I received from Charlie forced me to be consciously engaged in the act of playing- never outsourcing things to muscle memory.

I think that largely this was to avoid falling into mechanically playing over changes and to be actively engaged in thinking about the music at the moment it was happening and responding to it creatively.

Flow (as defined by Mihály Csíkszentmihályi) is between frustration and boredom because either the activity is too difficult or too easy.