Yes, if you're doing (real) mountain biking, which in my hood involves riding over slippery head-sized rocks and stumps down 30 degree slopes. However, regardless of your protection, if you come off of your bike in this terrain, you're almost certainly in for a bunch of hurt.
On the road, of course not. Even a slow tumble off a bike on pavement can result in a fractured arm/wrist/clavacle, or a fractured skull or broken neck, even with 'armored clothing'. The key is to never fall off of your bike, or hit anything, or let anything hit you.