Expect some benefits, like relaxation, with just one class.
“You can see basic health benefits after just one yoga class such as improved circulation, a sense of relaxation, and mental clarity immediately following (and even during) the class. Obviously the benefits are increased and prolonged the more you practice.” Krissy Jones  founder of Sky Yoga

Improve posture, fitness, and energy levels, and reduce stress in two sessions per week.

“If you’re looking to see sustainable health effects from the practice, I would recommend practicing a minimum of two to four times per week to start, and increase to three to six times per week. If you commit to a routine, you’ll start to see improvements in your mental clarity, posture, stress level, respiratory system, energy, metabolism, and your hormones will become more balanced. Yoga is best practiced consistently over a long period of time and is a longevity practice. Because yoga is not aggressive and there are so many varied styles and forms, it’s safe to practice yoga daily.”
If you’re unfit, you will see results more dramatically.

“If you haven’t done any form of activity and you start doing yoga regularly, you’ll see a dramatic shift in physique quite quickly. If you’re already fit and active, you’ll start to see results first in a reduction of stress and mental serenity first followed by more subtle results in terms of your physical appearance.” Krissy Jones
Ramp up to three session per week to see the tone building up in your body.

“Yoga is not a fitness program, at least the yoga I teach and believe in, but it is a wellness program. Having a fit body is part of being well but it is not the goal, it’s just a side effect. But once you commit to a regular practice of three or four times per week, you’ll start to see changes in your body. You’ll become flexible yet strong. Your muscles become toned but not bulky. And often times your diet will naturally improve when you do a lot of yoga because your body will start to crave healthier fuel.”

Would you agree that practicing yoga made a big difference in your life especially when it is paired up with consistency.  Depending on your body, you will know when you need to arive on the mat more than once or twice a week. Start easy without being overwhelmed and observe changes that occur. From there tailor a schedule that is consistent. If you want to be on the mat once or twice a week make a point to do it every week instead of coming 3 times in one week and none in the next.  Find your breath and gift yourself an hour just for you. How often do we do that?