Front and Rear Tires Different Heights

A buddy of mine purchased new Rear tires for his 800 xmr. He went wider and he went with 29.5 Outlaws. The Outlaw tires are about 1" taller now in the rear then the fronts with 29.5 SB. Will this affect anything? He was told it would and asked if I ever heard anything like that. So I thought I would find out.
Thanks.

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