That is what is called mutliwire circuit or shared neutral circuit.
It is a perfectly legitamate way of wiring, but a lot of people don't like it in residential wiring because many people don't realize that both breakers need to be turned off and a screwup in the neutral can cause upto 240 volts on some devices.
But with a little care it is fine. In fact that is just a subset of the type of wiring that runs from the pole to your house.
It gives you 2 circuits with one cable. Also it helps with derating where you have cable bundled or in conduit. It only counts as 2 current carrying wires. Where if you have two separate circuit you would have 4 current carrying wires.
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