The beauty of any home exercise program, including Beachbody's P90X, is that you are the boss. The program can tell you what exercise to do and when to do it, but ultimately, you can skip any workout you'd like. That said, if Yoga X wasn't important to the P90X program and didn't contribute to your results, it wouldn't be part of the program.
Yoga X is a 90-minute combination of ashtanga yoga, balance postures and stretching poses followed by an ab-centric series. If you follow one of the schedules included with the program, you'll do Yoga X once or twice per week, depending upon the particular week and whether you are following the Classic, Lean or Doubles track. The session is more intense than many typical yoga classes, and forces you to use strength, balance, flexibility and breath work simultaneously. Some people are tempted to skip Yoga X, especially if they have never done yoga before. Host Tony Horton was a difficult convert himself at one point, until he found how much better he moved and felt after incorporating it into his regular routine and decided to include it in the P90X.
General Yoga Benefits
People unfamiliar with yoga tend to think of it as being all about flexibility, but it is so much more in reality. The University of Maryland Medical Center states that yoga may help reduce stress, anxiety, pain, high blood pressure and asthma, as well as help relieve many chronic diseases such as cancer, diabetes and heart disease. The entire workout is conducted in a state of deep focus and concentration, and participants are taught to be aware of every part of their body at all times. This "shutting out of the world" is what contributes to the peace and stress relief practitioners report, and is a way of doing something just for you for a while.
Yoga and P90X
Yoga is included in the P90X mainly for the strength, balance and flexibility benefits. If you think Yoga X is your "easy day", think again -- the first portion of the workout is a rapidly-paced series of strength-focused vinyasas that keep even the most muscle-bound participants on their toes. Horton included yoga to teach you how to build a different kind of strength. Most of the postures involve isometric exercise, but also require a certain amount of flexibility. The flexibility component is important because the rest of the P90X focuses on muscle building. The more you tear down and rebuild your muscles, the more you must stretch them out to maintain a full range of motion. The balance portion of Yoga X is important because good balance reduces your risk of injury. The ab series, "Yoga Belly Seven," is a gentle but intense ab workout that acts as an adjunct to the "Ab Ripper" workout that you do three times per week to sculpt and strengthen your abs from every angle.
If You Skip It
If you decide to skip yoga, it doesn't automatically give you the day off. The benefits of yoga on that particular day are just as important to your results as the cardio or weight lifting workouts the rest of the week. An alternative would be to do about 45 minutes of body weight exercises like pushups, pullups, chair dips, squats and calf raises followed by a 15-minute continuous ab workout and an hour or so of thorough stretching. Of course, you could always just bite the bullet and do Yoga X -- you might find that you enjoy it.