Are you constantly being attacked by a horde of creatures and have difficulties deciding which one of them to attack back?
Plenty of professionals I’m sure would suggest you attack the closest one, but how do you know which one that is? In real life, blessed with the gift of sight you would simply look at them and try and decide. In Games you need to measure the distance.
This video will show you how to figure out what game object is closest to you.
What a great VR-ready tool for measuring between objects and surfaces and much more, then check out this tool from the asset store.
Want the absolute fundamentals of Unity programming? Then check out this highly rated Plural Sight course.