The phrase "to add this function" means to include or incorporate a specific feature or capability into something, such as a program or device. Full definition
For me, I know I'll finish a project if it's relatively easy and if the end result will not only look great, but will add function as well. (behr.com)
Many of the aesthetic touches also add function to the enclosure. (digitaltrends.com)
This location is perfect for both adding some interest to your bedroom walls, as well as adding function for your morning routine. (mysahomestyling.com)