My old '91 was starting to split at a spot welded seams in the rear of the bed. I took some photos but can't seem to find them now. It was due to the weight and extra force my WilderNest put on them, which have a pair of springs to prevent the top from slamming shut. When the lid is closed there's a force pushing the rear door to widen. The opening was held closed only by the tailgate after 25 years and there was a visible gap.
I have not gotten around to installing the 'Nest or bed side stiffeners on my Tacoma, but I do have a topper on it and haven't (yet) seen any indication that the beds want to open. I do plan to install something, the rear opening on pickup beds has been a weak spot since pickup beds have existed.
It can be exacerbated from particular uses but even if you never put on a topper or carry stuff against the walls it's still a huge unsupported void that moves with bed flex. My $0.02 is it can't hurt if you actually use your truck bed. I can't say one way or the other that it's due to the composite inner bed. It's plenty stiff but perhaps being a bolted rather than a welded arrangement it does factor in. The Toyota beds from '79 to '88 weren't welded double walls but my '91 was a true double wall bed, so I dunno.
ETA photos.
You can kind of see the way the gap opens from bottom to top:
It was cracking up under the bed rail and you can see the way the rail was buckling (this is where I bolted on a 1/4" strap to reinforce, BTW):