I've (seems like all of a sudden) had a bunch of big oak tree roots
"surface". In so doing, they're a nuisance to mowing efforts.

I have some that are longitudinal, maybe 1-2 long, way out from the tree
trunk.

Others are just seeming to emerge on the yard side of planter boxes around
the trunks. They're coming out just on the outside of the landscape timers
making up the planter box. These tend to be more knobby than longitudinal.

Some people tell me it isn't the roots emerging, but the ground around them
either subsiding or eroding away. I dunno which it is, and don't care (at
least I think I don't).

I do need to deal with 'em. The obvious solution is to get something like a
stump grinder in and "plane" 'em down.

Anyone see any huge reason not to do this? If it will significantly damge
the tree, then I won't do it. But, the question really is can I do that
without it much hurting the tree?

Sure will help my mower decks not to have those obstacles there.