1. You can rebuild (as in BT) immediately, without needing to build a 5gm. That is, you built for a flux on a Jebus Cross on 111 gm1, you have slow but no bless (or vice versa), and you rebuild right away (on the same day). Yes, it's expensive, but you have both slow and bless.
2. With a built 4lvl, you split for mana, having the necessary resources, the next day you build a 5gm and immediately rebuild it, and then go off wandering further.
I think there are quite a few such moments; in general, it's not all clear-cut, it needs to be tested in combat conditions.