With my plates, the docs expected to leave them in unless a problem developed with them. Didn’t have any problems so … the plates are still in. My plates were for an ankle however.
As a engineer with structural analysis experience, I would be concerned if the metal was left in place. Bones to flex under stress. With a stiff metal attachments, these may create stress increases at the attachment points that would create local stresses that are high enough to damage the bone.
Perhaps this would generate pain that would simply make you stop or reduce the effort. This probably is not a concern for most folks, but for those lifting weights or some other sports, leaving the metal in place could be a problem.
It all depends on how high the bone is stressed in the future. The metal represents a discontinuity in stiffness, and such things create local stress concentrations that create failure risk.
If the bone is not highly stressed, it would not matter.