In my approach to Hot Yoga, based on the Barkan Method, and called the Hot Yoga Evolution, we begin the class with 2-3 Sun-salutations. We think that doing salutations is a good idea for several reasons. Today, I will explain one of them.
The teacher is able to qualify the ability of each student, as well as qualify the ability of the students as a group. Qualify ability? You see, when teaching a student a particular posture, it is important that you have previously investigated their ability to "approach" the given posture.
Let me clarify with an example: imagine that you are in a first-time teaching situation with a particular student. You're going to get them to do Warrior II and Triangle (Virabhadrasana II and Trikonasana.) But the student has a "poor" (degenerated) hip joint, which only extends or flexes a little. If you are not aware of that limitation from previously observing the student, he / she will have serious trouble doing the Warrior II, no matter how good your instructions or demonstrations are! This is a very common problem in Hot Yoga today, especially for any teacher with students who are over the age of 35!
Therefore, to beginning your Hot Yoga class with a couple of sun-salutations is something that I highly recommend. You would be able to observe your students and gather information. You are able to assess their ability (qualify ability) to bend forward, back bend, lunge, etc. Most of the "normal*" people who attend your Hot Yoga classes today have quite serious (and often numerous!) ability limitations. If I approach teaching them without qualifying their orthopedic status first, I set them up for failure, inflammation, even injury or re-injury. In my teacher training programs, we always strive to help you improve the skills of reading your Students' bodies.
* "Normal" people—i.e. people who don't do much yoga, are not advanced, are just… normal.