Benefit of revolting from home city?

I’ve never understood the benefit of revolting. I can see that the resource cost is lower than aging up to V and you can ship extra forts, but losing your ability to gather resources besides factories or trade posts seems pretty bad. Plus you can’t upgrade your units to imperial status I believe. And it’s not like the militiamen that your villagers turn into are very powerful. Can someone tell me what I’m missing?