All the above rules should apply to simply supported natural timber beams in which stress and deflection are maximum at center span and near enough just in shear at the wallplate. Structural timbers built up as trusses, [usually factory made, that is triangulated assemblies using fish plates, toothed connectors, bolts, etc.], should not be cut or drilled at all. That's because the stesses are about equal throughout the length and across the section, usually with minimal bending loads in addition to tensile or compression. The stresses are high and the timbers are strictly graded for purpose. "Manufactured" lumber 'I' beams also need care when drilling if hole location options not marked by the maker.
