In game, freed happy pops make better workers and better soldiers but you DO have to make them happy and it's a lot of micromanagement of balancing their different classes needs and handling unemployment etc. Free happy pecialists make so much of whatever product, but they cost SO much in consumer goods.

Unless you use shared burdens, comrade! Liberate the galaxy, become the red tide of all freed pops, you have nothing to lose but your chains!