I don't know what the technical explanation for this option is. All I know is that if I do not have this option checked, the pointer is extremely unreliable. When it is not checked, if you do something like click on bandages and then click on something to apply them to, sometimes the bandage applies and sometimes it doesn't and sometimes the circular targeting cursor stays open. Also, when you move the pointer across the screen, it flickers or drags or just acts bizarre....like it's possessed or something.
It's hard to explain.
Unfortunately, when you switch between characters or accounts, sometimes you log onto a character you don't use often that doesn't have this option checked. If you don't do anything with that character other than just log on to get something (e.g., a gift ticket), you don't realize the option isn't checked. Then you switch characters to one you do use often and after a few minutes, usually when you're in a bad spot, you realize the darn option's not checked. Checking it then and there SOMETIMES fixes the problems. Other times, it seems as if you have to log out, completely close the client, and then log back in again before the client really seems to straighten itself out.
I have yet to figure out where the information for this option is stored so that it manages to reset itself across characters. You'd think once you checked it for a specific character, it would stay checked. But no.......every once in a while it just comes unchecked with what seems to be no rhyme or reason. Does a patch change it? Dunno. All I know is that sometimes the setting seems to copy itself from one character to another, but not the way you want it to (i.e., defaulted to be checked).