Maybe it's a setting thing but that doesn't match my experience with IK.

* I don't see any target. I see that in the documentation but I've never seen it on the screen. Maybe it is a setting that can be toggled?

* You can override the target by using the X/Y/Z controls to move the hand or foot. Whatever you dialed in is the new target and it matches the position of the hand/foot.

* When I turn IK on or off, the hand/foot stays in more or less the same point.

The circumstance where toggling IK on or off causing a figure to change pose is when the current frame is not a key frame. The key frames will recalculate to keep the same pose either with or without IK, but the way movement from one key frame to another is achieved might be totally different (and sometimes badly broken).

I've largely stopped using IK because, although it's easier to precisely position a hand or foot with it on, the animations often become jerky instead of smooth. (I wish hands and feet kept the X/Y/Z controls when IK was off!)