I have a junction box with two switches. One switch runs a light and the other runs a light and an exhaust fan (separate fixtures). The box has 4 cables entering each with black, white, and ground wires. I was surprised to see two of the black wires are pigtailed together with two other black wires before continuing to the switches. The other terminal of the switches are connected to the black wires of the other two cables. All 4 white wires are pigtailed together and all 6 ground wires are pigtailed together (4 from the wires and 2 from the switches). Is it common for two branches of a circuit to be bonded in this way? All cables are protected by one breaker.
Another surprising (to me) aspect of this circuit is that it is protected by a double breaker (not a tandem breaker). It was my understanding that double breakers were used to create 240V circuits for large appliances. The breaker in question is 15A on each arm and labeled "Hall lights" (which seems roughly correct). Why would a double breaker be used for such a circuit?
Finally, given that there appears to be two hot cables coming into the box and two load cables exiting the box, is it fair to assume that the two loads that are controlled by the second switch are wired together in parallel somewhere inside the walls?
My locale is Pennsylvania, US.