I asked this question in another forum yesterday and the replies I got made it sound like 285/70 could be run with NO wheel spacers as long as you didn't twist the Jeep up on the trail too bad.
But yeah, if you use less backspacing or spacers you're putting more leverage on the axle shafts, lug studs, ball joints, etc. There are videos floating around of bent axle shafts on JKO.
2012 Dozer JKU Sport
ACE rock rails
3/4" Daystar spacers/extra OE spacers up front
Airaid MXP intake kit
33x12.50 GY Duratracs on MB 72s