Installing a duplex plug next to an existing exterior GFCI plug...why?

http://www.VideoJoeKnows.com Installing a duplex plug next to an existing exterior GFI plug....why? Good question......but there "is" a good answer to the why re: installing a duplex plug next to an existing "exterior" GFCI plug. Do you know what the answer is & why "joe" would be doing this? GFCI plugs work pretty much like a regular duplex plug so why on earth would "joe" be needing to install another duplex plug next to an existing GFI plug? There's only one reason I can think of but it's not everyday anyone would need to install a regular duplex plug next to an existing exterior GFCI plug....or for that matter.....an interior GFI plug. Watch this short video clip & see what "joe's" up to.
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