Originally Posted by
Scooper
The main purpose of the bridge is, as unworthy1 points out, to reduce dynamic stresses on the BB shell/chainstay joints by adding some rigidity in that area.
I'm having difficulty imagining any stresses on the BB that would be mitigated by a little chainstay bridge, or how that location adds any rigidity.
The two purposes of a chainstay bridge are 1) a place to mount a fender, and 2) keep the tire from getting wedged in there too tight during changes.
Might help a little bit keeping things aligned when there's no wheel in there... but when there's a hub in the dropouts the chainstay bridge isn't doing anything structurual.