If I want to move an object and constrain it to the same X or Y position, I can hold the SHIFT key. If I want to duplicate the object, I hold the OPTION key.
In both cases, I have to click to select the object first. But then they work differently. I can’t press the SHIFT key until after I start dragging the object. On the other hand, to duplicate it, I must press OPTION before I start dragging. That confuses me.
If all I want to do is move the object, I can click the mouse button and move the mouse at the same time. I often try to press the OPTION or SHIFT buttons at the same time that I start dragging, and nothing happens other than creating a selection rectangle.
I’m sure that this works different in other applications, though I’d have to go and investigate to be sure.