It has some practical advantages:
Consider a remote switchbank - if you run 5V to it there are more places for an accidental short of the 5V to the ground (chassis?). Often the chassis can be the ground wire (in automotive wiring this is universally used) - thus saving a wire.
If you only route ground and switch input lines you have a wiring harness that can't generate sparks (another reason this is done in automotive environments).
There's also a bit of historical accident reason for this - the ancient TTL logic families could not be switched to 5V safely (resistor was needed) - but switching directly to ground was safe for the chips.