If you hide the Dock you may have noticed that when you then move your cursor to the edge of the screen to make it reveal itself, there’s a slight delay before the Dock slides back into view. The delay may not be that long, maybe half a second, but if change can be had why not do it.
In the Terminal there is a command can make the Dock appear instantly. From the Terminal, run the following command:
defaults write com.apple.Dock autohide-delay -float 0 && killall Dock
That will change the setting and relaunch the Dock all in one fell swoop. When you move your cursor to the edge of your screen now, the Dock should appear immediately.
If you ever want to restore the default delay, open the Terminal and enter the command:
defaults delete com.apple.Dock autohide-delay && killall Dock.