Modify this value if you think it is too short.
It allows users to select the page they will see when they go to your root domain e.g.
www.yourforum.com/, just like Home Page Route.
They can set it in their
profile=>settings page right under their theme selection, but only if you check that box to allow it.
The result is the same as the Home Page Route but for that user only.
Also, if a user does select a custom home page, it will override what you set in Home Page Route. Just like when a user selects a custom theme, it will override your theme selection.