When an Object is selected and you click something with the Eye Dropper tool you will change the strong of the selected object
Many tools show their options you double click them
You can configure it to copy or not and apply or not both Character Style and Paragraph Style
Command turns the pointer into Selection Tool so you can use it to select stuff and then release it to return to the selected tool. This is helpful for using the Eye Dropper tool.
Option-Eye-Dropper change’s it’s behavior
No-Option-Eye-Dropper is PULL IN from object
Option-Eye-Dropper is PUSH OUT to object
In other words you don’t have to select something to perform that modification