| I'm not sure I understand the question too well.....
but as far as learning stuff and committing it to memory I feel pretty strongly about it in certain situations.
I'm in the studio right now on a record date with Jem and we're doing four songs. I'm playing piano, guitar and bass on different stuff so my head is all over the place. It was essential to learn all the material no matter which instrument I am playing. I'm hearing these songs in their overall form way more than individual parts as I'm jumping from instrument to instrument. And that tends to help me adjust to each part a lot easier. I learnt the words and the melody first, and am crafting the parts around that.
It's nice taking a break right now while another cat lays down acoustic guitar parts on one of the songs so I can collect myself and get ready for the next song on piano.
In a live situation if I have the music ahead of time I will always commit everything to memory so I can interact with the band and the artist on a gig. but there are sessions I get called to play on which is all reading such as movie, tv, or just single track sessions for pop records and stuff. And sometimes it's not even reading, it's just being played a crappy demo with no words, someone strumming a guitar, and someone humming a melody. Then you have to not only learn the song from the demo, but come up with a part, remember it for each take, and improve on it each take if you can.
And of course the more you play certain styles and ideas, the less you have to think about them. Therefore freeing you up to be creative with a part as it evolves.
I highly recommend being able to read great, and also to be able to pick things up by ear quickly put parts together on the spot.
I hope that answered the question...? not sure, but that's how I feel about the subject, and it is super relevant for today's session in LA randomly enough.
Easy,
Janek | 
