Forgive me for asking, but what code is that quoted from? Is that by chance in D1.1? If so, any help finding it in the book would be helpful...as well as what revision you're referring to.
As for excessive reinforcement... what it does is it creates a larger "re-entry angle" which means that the toe of the weld would be a greater stress riser in the event of vibration or other stress occurrance.
In other words, if you take a piece of flat 1/4" plate, then a piece that consists of 2 pieces welded together at a 45 degree angle, the one welded at the angle would be weaker since it has the angle already there to help focus the stress, even from the first occurrance of stress...from then on, it is weakened and even moreso takes the majority of stress.
or another example: If you were to weld a thin bead across a plate, then bend it, most likely it would begin to focus stress at the weld toe. As is't slowly worked back and forth, that spot will weaken and crack (granted, all HAZ issues aside).