The Bite-Sized series of articles is meant to take the most powerful cards in Dominion and give a short explanation of what makes them powerful.
The split pile of Sauna and Avanto can provide three different deck control functions that are valuable in most games of Dominion: thinning, draw, and a village. In spite of the fact that it’s mediocre at providing each one of these effects individually, the fact that you can get all three of them makes Sauna/Avanto worth going for in many games, especially if it’s the only source or at least one of those effects.
If you’re using Sauna/Avanto for trashing, you usually want to go for other sources of trashing first, unless those sources are prohibitively expensive. In the absence of other reasonable trashers, you’ll either want to open Sauna/Silver and hope for collision soon, or consider skipping trashing that game.
If you want to draw cards with Sauna/Avanto, you’ll want to make sure you are in a situation to get lots of Avantos. Draw is what this pile is best at, so you’ll be in good shape if you build a deck to be ready for the Avantos when they show up. The main exception to this is when Sauna is the only village.
If you want a village out of the pile, Sauna is pretty unreliable and inefficient at getting you there. You have to line up three cards to get that effect, and get lots of copies of both Sauna and Avanto. On top of this, you won’t get all of the possible actions every turn. As a supplemental source of one or two extra actions each turn, or to support Avanto as draw, this is pretty good, but as the only village for supporting other terminals, Sauna usually doesn’t cut it by itself.