In the classical yoga sutras of Sage Patanjali, there are 8 limbs or stages. Asanas is the third limb or stage. The first two are the yamas and niyamas. There is some difference about how to view the 8. In Saiva Siddhanta, we view them as overlapping stages, whilst in modern American yoga schools, they're more likely to be seen as limbs. Personally, I don't agree with this POV as it seems more logical to have your ethical life in order before being successful with more advanced stages.
Most yoga studios more or less ignore the yamas and niyamas, or have never heard of them. (The old spiritual ego of 'I'm beyond that' comes into play.) They start with the asanas, and then some do take it further. Regardless if how one views it, it can't do a lot of harm physically unless you overdo it. Personally, I'm still working on the yamas and niyamas, and will be for the rest of this lifetime.