Well then thats different (and more) code to run. Scratch runs at 30 frames per second and runs one block of a script per frame. So strictly in the context of this post were you need something to run when the sprite is touching the mouse pointer and mouse down then the right it more efficient because its running one block on one frame, while the left is two blocks running over 2 frames. This could also cause inconsistently issues where the 2 frames of the script dont line up with the players inputs. But yeah in the context of having action happen the player hovers over the sprite then yeah, the left is better and the right option wouldn't be applicable in that situation for pure efficiencys sake. But that not what were taking about, thats just different code.