Earlier today I was proofreading the four pieces I'm writing to make sure I place courtesy accidentals where appropriate – as in where I deem them appropriate.
As the name implies, courtesy accidentals are just, well, a courtesy to the performer and technically aren't necessary.
In more chromatic sections, I think their importance rises. But I also think one has to try and combat instances where a musician might legitimately not know what to play – perhaps because the altered note is more ornamental in nature – or where that person might not know enough to make an informed decision as to what to play if there is a slight hint of ambiguiity.
In the excerpt below I was about to place a courtesy natural sign on the "g" in the bass voice of measure 3 as the "g" in measure 2 was a "g-sharp".
But then I realized I had already stated it was "g-natural" by specifying it would be played as an open string – considering that I didn't specify an alternate tuning. There are actually a few instances throughout the pieces where I think the fingering or implied fret position makes it clear what to play without the need for courtesy accidentals.
Of course, one could argue that I should place a courtesy accidental on the "f-natural" in measure 2 given that it was an "f-sharp" in measure one – albeit in a different voice.
But the guitarists in the audience already knew the correct note to play … right?