Community Codes are more than just pedestrian promo codes - sometimes, they also unlock special access to PCB:NG.
For example, PCB:NG using Community Codes as a way to check out early drops of software. A Community Code will also allow you to "jump the line" for invites, if we up an invite list for early access:
So even if you haven't gotten a personal invite, entering your Community Code let's you get one on demand just be entering it in the last field. Cool, right?