I guess the option is mostly for RP reason and also if you want to make them lose a habitat far from your border (e.g. in their home system).If you "dismantle" and later decide to replace, that is 5K minerals and some Influence wasted versus getting them for FREE when you conquer.
In order to get Scrap, you will have to bring a Scrap Hauler. Good luck getting one of those on the open Market. lol![]()