autoland
The Phabricator/Lando/Conduit system lands most of the changes initially here for integration and if there are no issues, they later get merged into production (mozilla-central) which gets served as Nightly builds to users contributing to testing.
If this tree is closed: Developers can still request their changes to land once the tree reopens. The longer it is closed, the more likely patches waiting to land will have conflicting changesets and the one which attempts to land later will fail to apply and need an update by the developer. The arrival of the code in production trees (mozilla-central) is also delayed.