There are three planes of movement – transverse, frontal and sagittal, and all movements in Crossfit (and in generally really) fall into one of these three planes of movement. Bio-mechanically, we’re built so that the predominant amount of movements are performed in the sagittal plane, with some degree of movements in the frontal plane; from a fitness and exercise perspective there are very limited movements that occur in the transverse plane.
All of this doesn’t really matter to the average beginner Crossfitter, but as the athlete progresses from beginner to intermediate and onto advanced, these planes of motion become increasingly important, in two specific ways. Firstly, neglecting the transverse and frontal planes by only focusing on the sagittal plane invariably leads to weaknesses in muscle development and endurance, which naturally leads to muscular imbalances which in turn can lead to injuries. Secondly, the body was designed to work across all three Planes of Movement neglecting one simply means you’re creating a weak link in the change which can inhibit training progress.
The good news is that because Crossfit focusess so much on Constantly varied, functional fitness, at high intensity, that is universally scalable over broad time and modal domains, this generally means that all three Planes of Movement are generally being trained across broad time and modal domains, even then however, I’d still argue the transverse plane in particular is notably neglected more than the others, however this can be supplemented with plenty of unilateral kettlebell, clubbell and macebell work.