Jose, I've encountered professional accompanists who, to my surprise, are not especially skilled at reading music, and instead, simply use the chords to improvise the accompaniment. I discovered that when I couldn't understand why the accompaniment to my song sounded very different from how I was used to hearing it in rehearsals / lessons with a different pianist, and I was having trouble recognizing my entrance cues. Were those unusual situations, or is it fairly typical for an accompanist to just improvise on the chords even when they have the full P/V/G sheet music?
Well... That happens too (unfortunately). Strangely, "those people" tend to be conductors (who used to be full-time pianists).
Myself, I will usually fill in an accompaniment - especially for standards - if the chord symbols are provided. However, I also ask the singer if they want what's printed on the page, or if they'd like something "fuller". -Especially since most "standard" sheet music doubles the melody in the printed accompaniment. *I don't "like" "helping" singer's with their melody line.
