My knowledge is incomplete as to what powers and restrictions you get with an amateur license, but I think the only real reason you'd want to use HAM mode in the US is if you wanted to operate on US 433 or maybe the 868 MHz block. Not sure if HAMs have access to the latter one or not, though. The 915 block is pretty permissive here for unlicensed use, so that's usually sufficient.

Also, if a node is operating in HAM mode, it may not be able to mesh with other nodes not in HAM mode due to encryption being disabled. I could be wrong about that as I haven't read into that specifically, but to my knowledge it tracks.