For all those wondering what the strap does I took a picture of my Daytona when it was only hanging from the rubber mounts (and not yet bolted to the cat) during fitting.
As you can see it hangs low at the back, because the hanging brackets are not centrally mounted.
So without the strap gravity will be exerting twisting forces on the joint with the cat.
It is perhaps fortunate that it's quite a robust piece of kit, but none the less this addition load will cause a premature failure.
Still you can use that as an excuse to upgrade the whole system!