Staked scrap decides the number of scrap you can grab, on your hand, before you claim (put in bag). For example I rob someone, my staked scraps is only 3, which means even that person has 100 scraps, I could only bring home 3 scraps. I can not grab more than that. Another example I had 2.7 scraps and I go to sleep. It will maxed at 3 scraps before I claim it, so there will be some wasted time because scaps already at max cap . The number of Scraps balance is unlimited, but the unclaimed, or on your hand, is limited by the number of staked scraps.
and the scraps in your balance are safe, can not be robbed. only on your hands (unclaimed) which can be robbed. You get 1 opportunity to claim whatever scrap is in your stash every 4 hours. In terracore the amount of scrap you actually generate is dictated by your Engineering level.