The more I play, the more I have respect for the tactical depth afforded by specialists.
For example, I invaded one of Craster's bases. I had about 15 drillers more, but he had a specialist (an Infiltrator) in the base he didn't want to lose. So he ran away -- put the specialist in a sub, left the rest of his drillers there to hurt me, and the specialist set off on a long journey back to a friendly base.
However, my incoming sub had two specialists on it. The first, Helmsman, allows any sub carrying them to travel twice as fast. So immediately after my invading sub took over the base, I launched half a dozen drillers, plus the two specialists, on the same route as Craster's specialist was fleeing on. My sub travelled faster, so I quickly overtook Craster's and captured his Infiltrator.
But my sub was still on a course for Craster's heavily fortified base, of course. That's where the second specialist I had on board came into play: the Navigator, who lets you change the course of a sub. As soon as I'd taken Craster's Infiltrator, I changed my sub to go back to a friendly base and escaped without any further casualties.