Originally Posted by
woodcraft
Mostly folks attach it to seatstay so that drivers can't see it much, but passing birds can.
More of a dull idea, IMO.
If one is short, there isn’t room for a tool roll or seatbag to be mounted on the seatpost at the same time, so one has to find another place to keep a light (or tools). I mount on the left side seat stay for exactly this reason, but you have to have a light with an adjustable angle mount. Planet bike lights even come with a separate clamp to mount on the seat stays.