I recently had a conversation about using battery grips. I have them for my cameras, but don't always use them. I do like them. A lot. I usually find it more comfortable to do vertical images with the grip. But it does add weight. And the camera can look more intimidating. But that isn't what I'm here to write about.
The other part of the discussion was about using two batteries in the grip. Isn't that reason enough to use the grip? I use one battery. No, it isn't for weight. I have two batteries. I figure that if I have one in the camera, when it runs down I can take it out, put in the other one, and put the first one in the charger. That way I can keep working. If I used both batteries in the grip they would run down together, and then I'd have to wait to charge them (one at a time). By using one at a time I can keep going.
Sure, I can purchase another 2 batteries. But, until then, I'll use one at a time. Battery life has been such that I haven't had the overwhelming need to get an extra pair.