The Long Road said:
Neeeeeeeeeeeeeeeeedlerrrrrrrrrr...
If you can aim, there is no use for the Needler. And every time Bungie released a new Halo, they said "We changed the Needler so it's useful now!" and it never was.
In Halo Reach, the needler is one of my top weapons precisely *because* I never needed to aim. Once an enemy is out in the open, fire roughly 5 shots to get his shield down, then 8 to 'splode him. It's so effective it's scary. I'd pull of double kills by releasing the mist at someone, then as the shots tracked the first guy, I'd whip out my other gun and kill a second guy. When used properly, picking up the needler can net you roughly 5 kills (at least) with full ammo.
Step 1: lure them out.
Step 2: release the cloud in the general area of where they're going to be.
Step 3: +1 kill
Also, it pays to learn to dodge the needler. VERY hard, and VERY unreliable, but if you can do it, the guy with the needler is boned.
My most recent example of unused and pointless guns would be any gun that isn't a plasma cutter in either Dead Space game. There's just no reason to use anything else. In DS2, the pulse rifle becomes a bit more useful, but even then I just waltzed through the game using the plasma cutter most of the time. In DS2 they even skew the ammo drops in favor of what you're carrying. By the last few levels I had no room in my inventory for healthkits because I had so much ammo. All it dropped was pulse rounds and plasma shots because that's all I used. Everything else was so lame or so expensive to fire that I just didn't bother. The stabby things and explosive stuff was either hard to aim, hard to find a use for, or just impossible to dismember stuff with. Besides the plasma cutter, the only other two "cutting" style weapons are the ripper, which feels too weak, or the line gun, which costs a fortune to buy ammo for (not to mention the pitiful stacks of like, 2 per slot).