Added Cold Damage
this support is useful, but for many only 5% of any and all builds, if that.
my build is very specific that i use this support for. its one based off as much flat cold damage that i can possibly stack. windripper, ice shot, southbound gloves etc.
this support gem alone raises my tooltip DPS by 38%...an enormous boost. its pretty much required because of the dps it adds, since i already have cold pen and wed linked.
the only other two supports that i can or could use is slower projectiles and hypothermia. slower projectiles i really dislike, because its only a 29% more boost in dps while also lowering projectile speed by half.
hypothermia im not the biggest fan of. great for freeze and dps at 39% more, but it will never apply on the first hit. most likely best support against bosses since they're the only thing that would take more than one hit, and thus would get any benefit. however bosses hp would be high enough that chill may not even last long enough to really capitalize on hypothermia more damage boost.
again added cold is useful if only for basically one build in the entire game. otherwise i do agree that with the many other support gems out there, especially so many that add "more" damage, added cold just falls short overall