Applications

This is a separate series showing all the applications of the form. 
Once you are studying from "Taiji to the Max" these are not necessary for your training,

as a lot of apps are shown in that anyway, 

but if you want to see all the possible apps in the form, then this is a great series.
Or you may be studying a different style, but have not been shown apps, 

so this could help you understand the form you're learning.