If the exhaust pipe is disconnected below the engine, there should be no problem. If the exhaust manifold is disconnected at the cylinder head, there may be some combustion flames or serious backfires that may damage some plastic pieces in the engine compartment. The balance of exhaust backpressure will be lost if the exhaust manifold is removed. You may be cited by the highway patrol for excess noise. You will likely not be able to pass a smog test because of a non-functional disconnected catalytic converter.