Spoombung, I am with you on this, I usually have the chord structure and orchestration written down, and particular bass parts tabbed. If I didn't have this aide memoir, after not playing a particular song for say 3 months, I would need to think about it all over again! its a memory thing, I am in two bands and need to juggle loads of songs and I am not lucky enough to be one of these guys that has a photographic memory and never forgets a song!
I can read and really must improve my notation and agree it is an essential tool, but at a practise when you are making changes on the hoof, notation isn't really an option.
Ignoramus of Hereford