Commercial Centre

The Commercial Centre is used to 'advertize' you as a player. With a level 1 centre, you may join an alliance. With level 3, you may create an alliance. As an added bonus, it increases the number of spots in you colony, at 1 per level (despite what the in game tool tip says). With a colony hub at level 10 and commercial centre at level 5 (thereafter you need all 3 rare resources to continue upgrading), you unlock a total of 11 spaces. It does require open ground to build, as well as 50 people (population) at level 1. It also requires 5 power per level (but no additional people). You also need a level 30 commander at level 5.

Once built to level 5 and you are part of an alliance, it is probably better to demolish it. It provides no additional benefit but uses 25 power and 50 people. Opened spaces remain open even if it is demolished, whether those space were built upon or not. To unlock the remaining 5 colony spots, you need lots of rare resources, and the implementation of rares makes this nearly impossible without paying real money for Advanced Trade Tokens (you need 1 for each rare type purchased, and 1 for each purchase of any rare). You could potentially only buy 3 tokens and get all the rares needed at once, if they are offered and someone can tell you what the final amount is. If you manage to acquire and hold a node for your faction resource, you could mine all your faction's rares, requiring only 2 tokens to be purchased. Getting those resources to every colony is another issue entirely.