They can provide the kind of value midrange decks or control decks lean on instants and sorceries for, while getting into the red zone and pressuring your opponents, punishing them for using ramp and card draw that doesn't affect the board
Misty Salon showcases how some Rooms can care about how many halves of a Room you have unlocked
Genesis Wave + Kamahls Druidic Vow Genesis Wave is still an effective place to dump, I dunno, 15-20 mana
And its hard to know where this wants to fit in
The Vermin Gorger provides us with a small number of life points, the Skirk Prospector with mana, the Goblin Lookout boosts the mob
You get to cast the copy as the triggered ability resolves (which is triggered whenever the encoded creature deals combat damage to a player), ignoring timing restrictions