Relaxing makes practice easier.
Over-efforting is accompanied by tension somewhere in the body (for me, usually in the head and face). Distractions aLeo almost always arise with at least some subtle tension somewhere in the body.
A relaxed body is not only a more comfortable and pleasant place to meditate, and more fertile soil for metta, it’s also a more sensitive instrument to detect—and then let go of—disturbances.