The functional movements of CrossFit tend to be bilateral. This is because, as CrossFit defines them, functional movements are unique in their ability to move large loads, far distances quickly. Of course, it would be easier to accomplish this functional movement using both sides of your body. BUT, unilateral movements no doubt have their place in CrossFIt. One helpful use of unilateral movements is in warming up. We of course want both legs to be firing, and if we warm up just bilaterally, we can't be sure that one side isn't taking more of the load off of the other side. Doing single leg deadlifts is a great way to make sure both legs are warmed up and ready, independent of each other. Flo demonstrates the single leg deadlift beautifully in the photo below. Notice the straight line from her shoulder though her hip to her heel.