Part of this is also just the options that first-rate actors open up for you as a writer or director that less capable ones cannot. If you think of the performer's talent as kind of a box that you can fit your narrative and emotional depth in, you just wouldn't try to ship something unless you have a box big enough to hold it.
If you have someone like Anthony Hopkins or Ian McKellan on hand you can give them long, baroque speeches and they will nail it. With a less capable actor you would be forced to keep it simpler because most of that stuff might sound corny as hell in less capable hands.