No, not "necessary" !! And if you want/need to make tighter turns and/or have less line out, add weight to the main line a few feet ahead of your cranks (ie "Pushing" ).
And as Cray has pointed out .... line separation is a key factor in keeping your lines from crossing &/or becoming entangled. And I would add that line separation in depths at which your cranks are running is also helpful. (as in keeping the forwardmost crank running the deepest, then slightly shallower on each following crank) That way you not only cover a horizontal swath of water, but a vertical one.