You're right about the cuts and tautness, but I do think the seam helps with the "A" shape of the tarp, especially when it isn't pulled taut. You can get a good straight ridge by only tying up the ridge ends and letting the sides simply drape. But, if you do that with a tarp with no ridge it tends to have the 'ripples' like in Goatman's pictures.
At least that's my observation when comparing the stock HH tarps to ones with seams. Besides the tarp that came with my HH, all the tarps I own have ridge seams.
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