Bypass question

I have a hotwater boiler. I have heard that adding a bypass between the return and the supply is a good idea. My pump is at the base of the return line. I have a three riser manifold on the supply and return side. but one is a stub on each of them and each has a globe valve. Can I pipe a bypass from the supply to the return - and if so, does this make sense to do? I cannot see how the flow will go in the opposite direction. so I assume if I do this, a third of the supply goes directly back into the return so it keeps the temperature up going through the boiler. Is that correct?