"Agki Strodon" said:
A roughed up surface holds better than a smooth one because there's
more glue in the between pieces volume, ain't it?

"Agki Strodon" said:
Spaces in glued up joints produce weakness because theres no glue in
the spaces to form a bond.

Forget the physics... wood fibers are held together by lignin and xylan,
woodworking glues mimic natural glues by bonding the wood fibers together.
That's why it isn't necessary for the glue to soak in and why a smoother
(planed) wood surface holds better than a rough (sawed/sanded) surface.
--
Mac Cool