For those galactic achievements that simply give you a one time bonus, like a general or free planet discovery, is there any reason to keep them after you finish? I started to watch a let's play where he destroys it without apparent ill effect. Isn't this a little... odd? Some give bonuses otherwise like the Galactic Intel Agency, which I assume you would lose the Diplomacy bonus if you destroyed, but maybe not?
So in short, any reason not to destroy these once done to free up land?