Doing the exercises back to back without rest between moves ensures you're working your legs as hard as you can in as little time as possible. Resting too often or too long only shortchanges your gains, so keep plowing through each superset or giant set without pause.
The single-leg Romanian deadlift/Bulgarian split squat superset is also an opportunity for you to address any asymmetry you've noticed in your lower body. If you notice that your right leg is stronger than your left, don't make it worse by using more weight on one side than the other. Choose weight you know you can do with both sides, and stick to it.