I thought I understood this, but a recent game made me wary:

1. I used to pay great attention to when a social project only had one week left to go, and then purchase it. It seemed otherwise I was "wasting" social energy on a project which, say, only needed few credits to complete; my entire turn's social capacity would be spent on that project, with the overflow being wasted. Now not so sure:
Is the overflow then kept in the form of extra cash? That is, if my social project X needs 2 shields left to complete in the next week and I produce 20 shields, will I only spend, say, 12 bc on that project and get my unused social money for that turn? Or will purchasing that last week for 12bc, so that I can use my full social allotment, make my capacity unwasted?

2. Similarly, I am unsure what the purpose of purchasing a ship with 1 week left has: I dont seem to get it any earlier then if I hit "turn", when I get it the following week. When I "buy now", I spend money but I have to wait till next week anyhow. (Thus is purchasing ships with 2+ weeks to go the only meaningful use of that option?)

Can someone explain this, please?

thank you