The previous behavior of the "Date Added" sort (that was deemed "inaccurate" and changed to respect the avatars' upload dates in build 1642) had a unique use case: manually arranging avatars in the menu by un-favoriting and re-favoriting them to bump them to the top of the list.

This was helpful for ensuring certain avatars would appear in a specific order (especially in wings) to keep navigation familiar and "mains" or other frequently-used avatars on top of the pile. A custom order mode would accomplish this through officially-suported means.

This could involve a simple "move to top" option in the client with a more intuitive click-and-drag implementation on the website.