I dont know if he had a good idea or not but my dad always put his trucks in 4x4 at least once every month to "lube and exercise the system" as he called it. I have done so on most of my 4x's since. Dont know if it helps but I cant see what it hurts
I drove a 60s model CJ5 with dual rear wheels for years. It had the closed front knuckles half filled with gear lube.
I never had to replace an axle U-joint. But, every so often I had to replace that high bevel Timkin bearing on top.
It used these strange roller bearings and races for pivots top and bottom where your trucks use ball joints or kingpins.
After the second time I replaced the top one, I was trying figure out why.
I had considered drilling and tapping a hole in the top cap to put a Zerk fitting in so the top bearing could be greased.
I packed it when I put it in, but there was no way for it to get more lube.
I suddenly realized that this design was from the old style Jeeps, without hubs.
None of the originals had locking hubs. They all used slugs or bolted on splined caps.
So, that top bearing was supposed to be splash lubricated by the U-Joint as it spun.
After that, I made it a point to drop the shifter into 4wd between red lights about once a day, and never had to replace that bearing again.