There’s a section for beginners in the the Ultimate Mass Workout, which suggests a break-in period of gradual intensity upticks before a beginner starts experimenting with X Reps (the book provides week-by-week instructions). Those gradual intensity upticks are necessary because it’s a good idea to have your nervous system up to par—as in learning an exercise—before you start adding intensity techniques to it. While it’s true that X Reps are very safe, much safer than forced reps because the movement is pulsing a few inches as opposed to straining and writhing through the full stroke, beginners need to acquire nervous system coordination to maintain control in a fatigued state (at the end of a set of full-range reps).
If you’ve been training consistently for a few months, you should try X Reps on some of your exercises. They can make a set exponentially more effective. They’ll help to further increase your neuromuscular efficiency, or nerve-to-muscle connections, so you get stronger as well as give your muscle fibers a new anabolic stimulus. That means faster growth—if you don’t go overboard. Beginners are usually extremely enthusiastic and can overtrain quickly. That said, don’t use X-Rep partials at the end of more than one set of one exercise for each bodypart (see the workouts in UMW). For example, if you do one exercise per bodypart for two sets, use X Reps on the second set only. They are intense. Also, be sure to use them at the correct point along the stroke of each exercise, for example, just below the midpoint of an incline press. [Note: The Ultimate Mass Workout lists the single best exercise for each bodypart and the optimal X-Rep position for each.]