This would be an order given only to fighters, and they would only attempt to repair if there is still a carrier bay in your fleet with supplies remaining. Currently if you set fighters to cautious and your carrier gets blown up, or it runs out of supplies, then damaged fighters will just retreat to the edge of the screen (essentially making them useless). Basically what this boils down to is that a carrier bay in some fights can end up being more of a liability than anything else.
I second this, but would expand it to all ships. It could be solved by adding a check to the cautious order that looks for valid repair modules/hangers, if none exist then ignore the order.