It's always bugged me that more often than not, a lot of the AI's planets are idle. (and all the while I'm slamming them with transports)
I've always thought this was a bug, in that most human players always have planets building something. My economy/research planets for example are usually building constructors or transports. Once I get too many, then I just make my top of the line medium to keep them busy.
Anyway, now I'm wondering if leaving these planets idle actually frees up money to go to your production centers. Does it? Does the money in parens on an idle planet get wasted, or does it just not get spent,. Does it allow more money to go where you need it?