In MP I believe if both have Lone Wolf, your limited to zero companions. If one has Lone Wolf, the other can have a single companion. In SP, it means your limited to a party of 3 instead of 4. I went Lone Wolf (on my tank char) in Original Sin 1 SP and definitely got some worth out of it. My tank had like 2.5k HP by the end and rarely came even close to death.
