Going to keep this simple to understand for new people coming in to this sport.
Heavy BBs= More wind resistent, carries more energy down range, and are generally more accurate due to high production standards.
If you are sniping, or use a high powered DMR, you're gun will most likely benefit greatly by using top end heavy weight BBs. From experience I would say use these if you are at or over 450fps with .20s Since they are very heavy you want to be able to reach your target. These BBs take a lot more umph to get going, but once they start moving they carry out some distance.
Also, the green is such that it is easy to spot your out going fire, to track shots. But trying to see where the shoots are coming from, is next to impossible.
Energy on impact, THEY KNOW THEY BEEN HIT
Best help you can by your sniper rifle.
I wish I could just, have a million bottles of this ammo. lol Never have enough.