Some people refer to Iyengar as the intellectual yoga. Others deem it the most physical. I feel badly that it's been sort of portrayed as this 'Get your groovy outfit, roll out your mat, put your ankles behind your head, and talk about how skinny yoga has made you,' because that's not the point. Each yogic form focuses on body, mind, and spirit. But they achieve their goals in slightly different ways.
Pacing is one difference.
People these days tend to think they have to break their back and sweat like pigs or there's nothing happening. But we try to wake people up. You can't see the nervous system. You can't see the breath. The effects of doing bad pranayama are very severe compared to the effects of bad asana.