Previously, when you set the front page, 403 page, or 404 page on /admin/config/system/site-information, Drupal would convert path aliases to internal paths before saving. For example, if you entered /home (an alias for /node/1), the config stores /node/1.
This could cause redirects to /home instead of / when the front page is an aliased path, and it tied configuration to internal paths and thus to specific content (e.g. node IDs).
As of #1503146: Aliased paths cannot be set as front page, the front page and error pages now save exactly what you type, regardless of whether it is an alias or a system path. If you enter /home, that's what will be stored in config. The issue introduces a new path matcher that fixes the redirection problem -- in our example, visit / will no longer redirect to /home.
The main "gotcha" here is that, if you set the front page to /home (a.k.a. node/1) and then you change node 1's path alias to something else, your home page will suddenly be a 404, and you will need to remember to update it in site settings.
The same idea applies to custom 403 and 404 paths.
