I thought the primary mission of options_left was to catch spelling mistakes.

(This is also useful if a PC logically ought to pay attention to this option, but isn't.) What about making PCSetUseAmat() use PetscTryMethod() and move the check of "-pc_use_amat" into each implementation?

I agree with Barry that it should be high level and make it there for any PC to use if they want.

Do we really want to leave the confusing option in place for all the PCs that don't have inner solvers?

It just doesn't seem that bad to me.