Question is simple, and in the title. But to expand a bit, I've been slogging through my game I started in 1.0.0 (it's taking me a while to do a 1600 base/I/A/A/A game, alright?
) and I noticed something interesting, and perhaps counter intuitive.
Production that is not used on one turn is rolled over to the next. Great. A godsend, really. However, it doesn't appear that when one switches to a Planetary Project that the excess production one has on hand is used. Instead it appears to be flushed down the drain, gone forever. Near as I can tell, at least. If I am wrong (esp as of 1.0.3), never mind this post. 
Now I DO NOT want to restart up the more-than-one-thing-at-a-time debate. So please don't mention the war bring that up.
But I do find it odd, and a very slightly irritating that thousands of units of production can be flushed away without seeing any use from it whatsoever.
I also realize that it might be a bit game breaky/exploity to be able to suddenly send, let's say, 6000 Accrued Manufacturing Points into Population or Wealth. That'd be an insane population jump, for instance, and could lead to all sorts of fun.
OTOH, well, those production points were never used. Plus it's a One Off event. If someone has spent 200 turns slowly building up AMP, I'm not quite so sure it is all that bad if they are able to dump them into something useful much later on. It sure beats fiddling with the Production Wheel every turn.