You can separate and go do different things (one can talk to an NPC as a distraction while the other loots the rest of the house), have one person get into turn based combat while the other runs around in real time, or gets into a separate combat encounter (and the 2 will merge if they get close enough).
The entire party needs to be together in order to switch between map areas (there are 4 or 5 large map areas in the game world), or to use the teleporter system (at least currently; there have been requests to allow people to use the teleporters independently within the same map). At a certain point in the plot early in the game you will be given teleporter pyramids, which will (among other things) let each character easily teleport to the other.
Is there a way to split up the party in a way that the joining player gets to control more than one character? Right now it seems my partner is only able to control 1 and I am unable to make any of the other characters follow his toon and he only gets to use one character during combat.
