Best Practices - Where to Add New Domains on Shared Server

I'm wondering whether I should be adding all add on domains to /public_html subdirectory where the Primary Domain is located on shared server or if it is best practice to add new domains to the root folder (folder outside of /public_html and separate from the primary domain).  I imagine there could be a difference in that there are more nodes to traverse, but I'm not certain.

I would like to know if either is more optimal for server performance.

Thanks in advance