Double-click on the Adobe Illustrator eyedropper icon, and you get a useful panel of advanced options that allow you to control what it picks up and what it applies. Two columns, 'Eyedropper picks up' and 'Eyedropper applies'.
You can set it to pick up things it doesn't apply, and apply things it doesn't pick up. This seems like a useful feature, but it doesn't behave as I expected, and I can't find any case in which it makes a meaningful difference.
I thought that the purpose of this would be to mix settings. So, you could set 'Pick up' and not 'Apply' for something, and fill up the eye picker with that setting. Then, you could reverse the settings, tick 'Apply' and untick 'Pick up', and those stored settings would be applied whatever was clicked on with the eyepicker, alongside whatever other things it was set to pick up. But it doesn't work like that at all. Here are the results of some experiments...
These show that, when an item is selected and the eyedropper tool is used to grab the appearance of another item, 'Eyedropper Applies:' settings appear to make no difference.
My expectation was: nothing applied to A in Panel ii, blue fill black stroke applied in panel iii (picking up the blue fill, then applying the new blue fill plus the black stroke it picked up earlier from memory), and blue fill black stroke applied in panel iv (both from memory). However, in all these cases, the 'Applies...' settings seem to make no difference, and the 'Picks up...' setting appears to control both what is picked up and what is applied.
It's like the 'Applies' settings aren't there. But they must do something.
Can anyone give an example of different 'Picks up...' and 'Applies...' settings doing something useful that illustrates the significance of these two different settings and how they work?