It's interesting to see how misinformation propagates. The second-highest-rated answer on Stack Exchange (46 votes and climbing) claims that another reason for the left arrow cursor in early GUIs was to put the hotspot at (0,0) to save time in the mouse position calculations: http://ux.stackexchange.com/a/52349/43259 The answer cites this Reddit comment as its source: http://www.reddit.com/r/explainlikeimfive/comment…
This hit the BS detector for me too, mainly because it goes against some of the rules of thumb I have found useful for optimization. For example, the need for smooth and stutter-free ui notwithstanding, if something only happens in response to user input you are less likely to see important gains from this sort of CPU microoptimization. Even on a very old machine, it should be obvious that the computer adds integers much faster than you can move your finger (otherwise there would be no point of having the computer, am I right?) On the other hand, if you had to compute more on every frame or for a substantial amount of onscreen objects, that's where the real gains are going to live, because the numbers add up much more easily.