List variable for performanceTiming plug-in
I'm trying to understand how to implement the performanceTiming plug-in and it says a list variable is needed:
"If you wish to utilize the asset load time functionality within the plug-in, you must pass in the name of the list variable to be used."
What is the use case for using a list variable with the performanceTiming? If I don't use a list variable, then what information will I get?