Song Composing

Again, not really. Knowing exactly what you're doing can make you a very limited player/composer. Like me, I know all the keys/scales/modes and everything diatonic. It can end up sounding pretty boring if there's nothing unique or out of the ordinary sounding because you know what to expect.

Obviously, there is an art to getting diatonic stuff sounding good but if you're always correcting yourself, it'll be harder to come across "mistakes" and "bad" notes that actually end up sounding better than whatever it was that you meant to play.

THis is where the Creativity part comes in.
When playing all diatonicaly it helps you set a mood and atmosphere in your peice. Throwing the "mistakes" or whatever add alot of tension, and then going back into the scale adds release which is a huge part of making music and soloing. Its just knowing when to stay in key and when to venture out of key.

There is no wrong note in a song, you are always a half step away from a diatonic note, and playing a half step before the proper note adds tension and release.

P.S. and when soloing, how often do you think "I think I'm going to run up the Phrygian mode in thirds then I'll do some minor arpegioes". You don't usually have that much time to think when improvising :p.
 
P.S. and when soloing, how often do you think "I think I'm going to run up the Phrygian mode in thirds then I'll do some minor arpegioes". You don't usually have that much time to think when improvising :p.

That's what slow bends are for, not just for the sake of phrasing, but to actually think what to do next.