Do you ever see Players hold back or delay when their action or abilities aren’t needed? Do you, personally, hold back or delay when you aren’t really needed?
Yep, all the time, to both questions.
Nearly everyone in my current game group- a combined gaming experience pool of at least 160 years- delays or holds when they can't do anything when they come to the fore in the combat round cycle.
Its one of the factors by which we avoid the "15 Minute Workday," as I've mentioned several times.