I just realized when I did my gig tonight (reading charts in a General Business-Wedding Band I was subbing in) I would read but I was also making some instantaneous editing, if a part was too busy I'd leave notes out. If it felt better to change an octave here or there I'd do it. Over time I've come to look at the chart/part as a guide and rely on my experience to decide just how literally to take it. This has just come with experience over the years, but if need be I could totally read the part. It's just that on the fly I rely on my ears, taste and the interaction with others to play what works the best.