Grokus is extremely tough. He has a lot of health and can suffer extreme damage from defensive towers before dying. So, they can be an alternative to Crabatron in the Bunker (more health and damage while only taking up 10 more spaces). As he is a looter, he goes after Resource Pods, Harvesters and Under Halls (or their above-ground counterparts). You can clear a base by Grokus Bombing it; some Grokus can loot all the resources while the rest suffer all the damage from towers. Pairing Grokus with Sabnox or Balthazar is a good idea.
Though Grokus has less than satisfactory damage, it is still much better compared to the other looters.