The Rector is a repair and resurrection bot which can turn wrecks into brand new units, or reclaim them to get back your metal! It is fast, cheap to build and stealthy to radar. Therefore it's an effective method for reclaiming trees, rocks, structures and other reclaimable resources scattered across the map.
It is prudent to combine resurrection bots with attacking units so they can repair and either resurrect or reclaim wrecks to keep your army reinforced.
Managing to resurrect a constructor of another fraction is a way to obtain their particular technology.