In Civ5 there's a traditional pillage-and-fix strategy, you pillage enemy tiles and fix it with builders, then pillage again. You yield 10~20 Gold for every pillage-and-fix group per turn, which is quite a reasonable gold resource In Civ6 the pillage yield is very high, 50 science/100 gold per tile or so. But you can only pillage once since you cannot fix enemy tile, nor can you pillage your own improvement. But Rise and Fall solve that problem. Your border cities will flip to independent every 5 turns or so in Dark Age, you just pillage the tile, take the free city, then fix the pillaged tiles until the city becomes independent again. That yields 200 Science per 6~7 turns per group, suppose there's 4 mines to pillage, with the double pillage card. Which is a vast amount in early eras. Also, such operation can be done with multiple groups. So you get lots of gold, science, culture and faith from multiple pillage-and-fix cities. All you need is a builder, some troops, and a border city with low loyalty. You may want to make that city as disloyal as possible to speed up the pillage-and-fix process, which means a Dark Age is needed. That's really another nice bonus for Dark Age, ensuring it a better option than golden or heroic ages. I don't know why, but the expansion seems to tell us "Dark Age is the best age." Consider controlling your era point less(without affecting your other progress such as science and culture speed) is more difficult than getting more era points, this may be reasonable?