Ah I was wondering this too. Until it hit me. The Gunsmith and other vendors offer relatively unimpressive guns. But upon looking closer, each one of these guns offer different stats like rate of fire and range and so on. So where would these guns do well in? The CRUCIBLE! Hear me out.... When you play crucible, (and Iron Banner, heh heh..jk) everyone's stats for weapons and armor are basically leveled out. Everyone seems to be on the same playing field. The only thing that is different are the stats for your guns.(as in range, rate of fire, stability and so on) This is where these common and uncommon guns come into play. If you can find a regular, common gun with superb range, rate of fire and stability but lack luster damage, keep it! That damage does not matter in the crucible as everyone is the same. The ONLY difference are weapons that have that one or two perks that carries over, like the Thorns lingering damage, or the Incentives regenerative ammo that I would consider bringing that along instead of a common. Now when i go into crucible, stats on guns, are all that I look at. Give it a try. You may be surprised with the results.