Sometimes you need to have data from higher levels of hierarchy.
Let's check an example:
Inside a Feature you want to see related Objective. There is no direct relation between Feature and Objective, but the are connected via Epic.
Lookup Field in Feature helps to extract some data from Objective via Epic. Here is how you do it:
After that you will see Objective field inside every Feature and it will be set automatically if Epic has an Objective:
Lookup Field is very useful concept to access data from high levels of hierarchy.