Don't just drop his shield -anywhere-. I mean, you can, but it is far more efficient to know how the shield works. It blocks enemy damage and prevents it from going in or out, but friendly damage can travel through. So if you want to attack a bunch of enemies on the edge of an area, it makes more sense to jump a little in front of them, drop the shield, and shoot without advancing. But, you can also jump into a group of enemies, drop the shield, and immediate withdraw so they're in the shield. Those familiar with exactly how it works would run out before wasting ammo, but just like with Zarya's shields, it can always bait people who aren't thinking too much into wasting ammo as they take damage.