I know that if I leave Dead Machines about for Scrappers and Glinthawks they will come up and process/destroy the loot.
When I fight Shell Walkers what I always do is remain hidden as I destroy the camp that hold their Cargo, wait for them to reattach it by using their arm and then destroy the arm, generally by then they are weakened enough to quickly dispatch. I generally check the cargo after I've killed off all the machines in the area.
However, I am wondering if I am losing out on loot by waiting until I clear the area via them reattaching the cargo, similar to how I can lose loot if I don't loot the dead machines before Scrappers or Glinthawks get to them?