It goes wherever the cutting edge is. If your holder doesn't have a cutting edge, place it whichever way you like, no one cares.
Darvond: Actually, I was wondering why nobody has made a vertical holder.
I have a vertical holder. The paper unrolls and falls off in spirals, if the cat doesn't get it first.
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Anyway, roll placement is a matter of genuine preference and is thus not so much
absurd as
pointless to debate.
An actuall absurd debate is the damn toilet seat, because it
does have an optimal solution: unless you use a lid (in which case close it), don't fuck with the seat after doing your business.