dpb wrote:
....
Actually, they're laminated (normally 3-ply) but they're quite thin so
there's not much material there. It is that additional cross-grain that
is what little actual strength difference there is which owing to the
size isn't really all that much...

And, of course, in the case of pine or similar, that the biscuits are
birch or similar wood of somewhat stronger properties--but they're still
small in comparison so it's a minor effect.

One last note is that they can be used in places for mechanical strength
where otherwise there wouldn't be any--end to side grain, or other
places where a long to long grain joint isn't possible...

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