Too many people spam a whole map (in DM, especially) with the electro balls. A lot of noobs do the same thing in CTF within their own base. It's quite obnoxious. Some people do this just to mess with others.
I don't see any usefulness in the game to allowing electro balls to continuously flow out without limit. Secondary mortar doesn't have the same problem because it's secondary fire rate is slower. What if electro balls could only come out, say, 5 at a time? Then you have to wait a second for it to recharge.
I dunno the exact timing, but it appears as if it takes about one second to shoot out 5 electro balls. What if you could only shoot 5 balls within 2 seconds? Then you wouldn't be able to shoot them constantly.
Also, you have to release the right mouse button and press it again to shoot out more balls.
It seems as though this timing would not get in the way of doing electro combos. If I shoot 2 electro balls out and fire the primary, and then do it again, that takes about 2 seconds, so my "electro ball" limit resets to 5 and I can keep going. I would be able to continue doing electro combos without any hesitation. But this would prevent me from holding down the right mouse button and flooding a room with electro balls.
Perhaps it could be a cvar setting so people can switch it back if they are wanting to do some explosion tricks for a demo or something.