Being grounded after landing at an outstation with no maintenance available and having the aircraft unavailable for a couple of days while engineers are brought in comes into the equation.
When one system fails the remaining back up is under higher than normal load which may cause additional failures, like opening a can of worms.
Whilst the Airbus A320 has three systems, one of them, the blue system has much lower capability than the other two and is basically a last resort emergency back up which does a bit of work to help out the other two.
Flying on the RAT is a Mayday situation and the emergency services will be standing by as you land.
Due to Airbus fly by wire being so heavily dependent on electrics and hydraulics, a higher than normal level of redundancy is required and provided for.