Background Patterns are a great way to add visual interest to a motion graphics piece. You could make then easily in Adobe Illustrator. Making them in After Effects however, allows to opportunity to get into shape layers using the repeater function.

how to create different patterns using Shape Layers in After Effects. 

Here, Ukramedia’s Sergei Prokhnevskiy shows how to do just that. Sergei shows how to make a few various background patterns in Ae, from the simple to the more complex. All however show of the power of using shape layers in Ae, and how it can be pretty fun to experiment with the repeater function.