It's not that it's going to break anything as there is nothing locked together. It's more of a drag concern on the vehicle, with very little concern for wear of items since they are engaged (ie. bearings, seals, cv's, boots, etc.). Most of these items are not in motion constantly so wear will occur. Now to measure the wear is something else and have an accurate measurement forget about that!! LOL.

But a need to replace a cv boot, rather than the cv itself, could be argued due to the rotation of the shaft and constant stretch and compression during turning.

Think of it like why does the front tires wear when they are not driven (if driven constantly straight)? Why does the rear tires wear on a front wheel drive vehicle? Drag is a wear item.

So nothing stops from doing it, like every other 4x4. The boots last forever on front drive cars and my Mazda had 260k miles and was part-time and full-time and never replaced anything but gas. I had lockers front and rear and they engaged when I put it in part-time and stayed unlocked in full time or 2wd. I think I will install Air-Lockers and install them the same way. It worked great and never caused a problem, I just installed a manual over-ride button for those times when I needed the back to be locked.

Remember the manuals are written for idiots!!  If they didn't say that then someone would lock their hubs in at the start of winter and unlock them in the spring if they remembered.  It's just the manufactures covering their buttox.

If its a snowy type of day and you think you might want 4wd then lock them in.  As soon as the conditions are better unlock them.  Your more likely to rip a boot wheeling than you are turning the axil shafts just driving down the road.

I've gone 4wheeling where you might have to go 15 miles between trails.  I've just left the front locked and ran in 2wd.  Just a little slower.

I think he has a Sammy so he shouldn't have to worry about boots anyways.  Some of the really old Jimnys over here don't even have hubs.  They just have kind of like a metal plate with splines in it that bolt directly on to the axle.
 
But, in a Tracker after lifting it the CV joints are at a constant angle putting more stress on the CV boots therefore causeing them to tear more easiler.  Thats one of the reasons why I keep mine unlocked.  

I think he has a Sammy so he shouldn't have to worry about boots anyways.  Some of the really old Jimnys over here don't even have hubs.  They just have kind of like a metal plate with splines in it that bolt directly on to the axle.
   

LOL I ran into one of those bad boys in the junkyard, trying to find an SJ30 transfer case. (but it was too old and had the smaller xfer case mount ) And just throwin my 2 cents in, I don't leave mine locked.

Out on the trail I leave mine locked.... When I get ready to drive home Ill unlock em.

Later,
Bill