I've heard of people breaking 21 spline inputs with the front case in low and the rear in high.  According to the guy he wasn't even doing much when it broke.  Maybe it was already twisted and getting ready to go from prior hard use but I try to leave the front case in high until I put the rear case in low.

Just an opinion and I do run my front in low from time to time with the rear in high but not when I'm getting on it.

When I get my gears I'll probably order a 23 spline coupler at the same time and do 23 spline gears so it's one less thing to worry about.