Who said it was?
I've used KD construction lumber for plenty of benches, shop shelves, clamp racks, etc... It works just fine, as long as a furniture-like appearance isn't desired.
I wouldn't use KD doug fir or spruce for a fine woodworking heirloom bench, but it's fine for keeping the planer, miter saw, or clamps off the floor.
Barry
Way back when Builders Square was still in operation, they supplied kiln dried lumber, but I would bet at least 90% of the construction lumber in SoCal is "wet", but NBD.
Stack it up in the SoCal sun for a couple of weeks and it is bone dry and hasn't warped.
At least the stuff I buy hasn't warped.
Coming from the Midwest where kiln dried lumber was standard, I asked about why the SoCal lumber was wet.
The answer I got was that Doug fir could be used wet without problems, but not Spruce which is why so much of it shows up back east.
YMMV
Lew
Lew
Out here around Balmore/Washington DC all the constrauction grade lumber is kiln dried to ~ 12%. Green lumber would rot on the shelf.
'Kiln dried' lumber is not all dreid to the point of maximum stablity. COnstruction lumber, even when kiln dried, is typically NOT kiln dried to stability, as cabinet lumber would be.
As OP noted, that is usualy fine for utilitarian workbenches and sawhorses.
The big advantage for me is cutting the mortise. With two laminated boards, you can cut half the mortise out of each side with a router before glue-up rather than using a forsner bit and chisel, and you've got very little tuning up to do when it's laminated. Never tried the L-shaped legs, but that makes sense, too.
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