Some situations that may happen during moving day is that you are also more than willing to lend a hand to move a furniture or washing machine. However, as good as your intentions can be, you can delay the job of the movers.
They are an experience team, and while they appreciate the gesture, it might also be dangerous and can create obstacles when they work. You might get injured when lifting something, or you can harm someone as well. It is better if you stay out of the way, and let them to their job.
Of course, you can be present to answer any questions, or to direct them to the correct rooms. But when it comes to moving heavy objects, if you let the movers do their job, the things will go as smoothly as it can be.