My Tundra also said to run in 4hi for ten miles every month. At that time I lived where I had a 1/4 mile long dirt drvieway, every day I'd drive out in 4HI, and put it back in 4HI on the way in.
With my Ram, I use Auto 4wd enough to get things lubricated, even though it's not a "requirement" per the owners manual. If I didn't have the Auto mode to use when on the street, I would probably do what was mentioned above and toss it in 4HI in a good rain storm every once in a while, and keep the wheel straight as possible.
The benefit of running the 4wd system is for the front diff fluid lifespan. When fluids sit, and you go through temp cycles with the weather, condensation builds up inside the diff case (or engine, or trans, or tcase, whatever enclosed case isn't being used). Running the diff gets the fluids circulating, and then the temp burns off some of the water content from the condensation. (Some, it's not boiling out steam or anything). This is also why it's good practice to change any of your fluids when they are warm, so that the water content will come out with them instead of sticking to the walls of the case.