The so-called «29 inch» tire size is not actually a new size, it is just a new marketing term for 622 mm (700C) wheels with fat tires.

This size is probably a good option for taller riders for off-road use, compared with 559 mm (26 inch decimal) wheels. Larger diameter wheels don't sink as far into holes so they will give a better ride in rough conditions.

For shorter riders, wheels this large will cause unfortunate compromises in frame geometry, so they're probably not a good option for riders of short or medium height.