AutoHotkey calls a function in the Win32 API, which should not return until the clipboard is set up. You should not need to sleep after setting the clipboard data.
Often the script will need to rest after sending Ctrl+C, since if it doesn't, the process you are sending Ctrl+C to won't have time to modify the clipboard. In some cases AutoHotkey might sleep automatically, but in this case it doesn't matter, as ClipWait will sleep until the clipboard has data. It is not necessary to use Sleep before ClipWait, as long as the timeout of ClipWait is sufficient.
However, you may need to Sleep after sending Ctrl+V before resetting the clipboard to its previous value. I found that on my old Athlon XP 3000+ (2.2GHz) it was not necessary, but after upgrading to a Core 2 Duo (2.4GHz), the script would frequently reset the clipboard before the other application had processed Ctrl+V.
This also depends on the method used: it happened more often than not with SendInput, but never with SendEvent or ControlSend. SendInput is otherwise my preferred method.
Quote:
all ahk commands are call to a system process in order to execute the window API function
On the contrary, some commands are implemented with C run-time functions (which may in turn use OS features), and a few others purely affect program logic, and do not use any Windows API. Additionally, I think nigelle was suggesting AutoHotkey might call an
external process (i.e. an executable file), whereas in nearly every case AutoHotkey does not do this, so will not suffer from process priority issues. Commands like Run, Reload and Edit launch external processes.