In general going down the evil route should add more companions, and camp followers. Not really ones that are super fleshed out the "main" path companions, as I think Lae'zel, Shadowheart and Astarion have enough there to justify losing Wyll, Karlach and Halsin.
But it would be fun if the evil route gave you the vibe of building your own evil army to oppose the absolute for your own nefarious goals.
