A properly seated and oriented heat shield is also important for ensuring the pad meets the rotor squarely or with just a hint of leading edge slope. This is needed to minimize and squeal or chatter with the pad.

Best case is no impact at all.

Worst case (assuming an intact dust boot) could be the pad doesn't properly contact the rotor and reduced effectiveness or uneven braking.

It's worth checking out while you're thinking about it. Pad wear or squealing could show up later.