rottydaddy
En-Route
Why not read back the instructions.
"Bugsmasher 345, immediate left turn two four zero, vectors for traffic."
You think you hear three four zero and just say "Roger" or Wilco." Doesn't really help that much.
If you reply with, "left turn 340," the controller has a chance to say
"TWO four zero."
In controlled airspace, anything to do with heading, altitude, squawk, or runway should be read back, IMHO.
But using "Wilco, (and tail number)" for, say, S-turns for spacing or somesuch, is acceptable. "Roger" (and tail number) for something like an ATIS update when in the pattern is also acceptable.
"Roger, Wilco" is redundant... strictly Hollywood BS.