Why would you want a truck bed rug, especially if you already have a liner of some other type???
Well every bed liner material has advantages and disadvantages. Even a spray in bed liner is subject to damage and it's slippery too.
That way it's not such a big deal if it gets abused or even damaged a little. Not to mention that it's so cheap that adding one costs very little.
That's protection 2 ways. Carpet is the perfect surface for many kinds of hauling. Think about hauling furniture for example. Carpet is perfect for protecting cargo, even better than a spray on liner surface for one.
But it's protection another way too. It's protection for an expensive spray in liner too. A BedRug carpet mat for example costs about 1 tenth of what a professional spray liner will set you back. That's cheap protection... for the Bed Liner.
Neither spray on bed liners or drop in bed liners are particularly good at keeping cargo from sliding. A simple cheap carpet piece does the job better.
A liner that's hard is rough on the knees if your truck use puts you on your knees. A cheap carpet can save your knees while it does all this other stuff.
Permanent is often good. But permanent liners are always there. With a cheap carpet rug or truck bed rug, you can take it out any old time and be back to your main liner. It's an optional coating for you bed if you need it. If it isn't needed, out it comes...