I've found that when I'm setting up multiple cursors using multiple Ctrl-LeftClick operations, I'll sometimes get a cursor located in the wrong position (usually off by one character). It would be nice if you could remove errant cursor instances by simply doing a Ctrl-LeftClick on them again. In other words, make Ctrl-LeftClick a multi-cursor toggle. As it stands, I have to start over, or live with whatever changes get made to that incorrect location and fix them up afterwards.
I'm not sure how this would or should extend - if at all - to other multi-cursor or multi-selection operations.