I have a 29er with 29 x 2.25 tires and a 27.5+ bike with 27.5 x 3.0 tires (almost equal diameter to 29er).

My 29er I have to pick my lines riding single track. If I don't then the tires, more often than not, slide off the trail features which may or may not result in a dismount/crash. With my 27.5+ I just roll over obstacles and don't think about picking a line.

27.5+ is about better traction and roll over.