Patanjali's version of Yoga is quite different than "modern postural yoga". So is this text still meaningful and relevant? I think so. However, you have to do a little translating to make the text culturally and historically relevant.
For example: The most popular sutra on Asana (and one of only 3 sutras on asana!) says:
2.46 Sthira-Sukham Asanam
Loosely translated, this could mean "the seat should be steady and easeful" but let's unpack it a little bit more...
Asana – often translated to "seat". Asana can also mean abiding, dwelling, inhabiting. The emphasis here is being present, grounded and committed to whatever you are doing when you are doing it.
Sthira – steadiness, strength, to stand or to be firm. It has a relationship to the Sanskrit word Asthi which means bones. Your bones are the support for your body. In posture practice, when you align with the architecture of your bones, there is release in the muscles and space in the joints.
Sukha – Often translated to easeful or joyful, agreeable, and gentle. The word literally breaks down to "Good Space". When you first create steadiness through your bones, then every movement has grace and ease. The joints sing with space and the muscle sigh with support.
Want a little more insight? Here is a 15 minute lecture about Patanjali's instructions for "Asana" and how you can translate it for your practice. Below the lecture recording is a Home Practice MP3 based on a Stira-Sukham class from Yoga Club.