Pretty powerful I guess. I mean, teleportation is instantaneous movement of stuff.
I can imagine a teleporter being able to instantaneously rearrange the universe to simulate time travel or dimension travel. I can also imagine them being able to escape black holes or creating wind by teleporting air molecules around and thus forming a difference in density and pressure. They might also be able to teleport energy, so they could overcome inertia to instantaneously create stuff from other things, alter the momentum of stuff, etc.