I got stopped during hunting season a couple of years back by OPP. No big deal, but they asked to see guns and they asked me to pull out one of the rifle cases. Yes, sir, no problem. So I pull it out, put it on the ground at the side of the road - step back. They say - "That case is not locked" I say, "no sir, it is not locked, nor does it have to be sir" so they open the case "these firearms are not trigger locked" says the officer "no sir, you are correct, they are not trigger locked as I am not obligated to have them trigger or case locked as they are being transported" Then they start talking about how they "really should be in a locked case" so instead of arguing, I pulled out my PAL and offered a registration certificate for each gun. That got them back on track and showed them that I knew what I was doing, even though I am not sure that they did or if they were fishing, or whatever. They let me go right after very casually glancing at the certificates, thanked me for my cooperation, etc. And I am not criticizing the police in this situation although it did appear as though they could benefit from a refresher about the act, that's for sure.
My point is that there may or may not be real consequences to not carry the certificates, but it may help the interaction with LEO's or whoever.
And let's face it, if you are being asked to produce papers, it is likely because they are having to talk to you about something that you did to attract their attention. So the easier you can make their jobs and the less reason you give them to charge you with something the better, so that's why I carry them, even for the non restricteds. I also now have those one page "transportation and storage of firearms" guides from the RCMP everywhere - one in the car, one in each case, in the safe, in the cottage, etc. If I have to explain how things are supposed to work I will have one of those sheet to offer up if I think it will help.