After— ordering. This unit’s start job is queued after A’s start job finishes, regardless of whether A succeeded or failed.Wants=A— causes A to be started (if it isn’t already). Tolerates failure. No ordering.
They’re orthogonal. You usually want both together: Wants=foo.service + After=foo.service means “start foo, and start me only after foo is up, but don’t fail if foo fails.”