The “force-free” (FF) approximation has often been evoked as a convenient means of treating electromagnetic processes of extracting rotational energy from pulsars and black holes through their magnetospheres, to energize a variety of activities in the environments. In order to produce relativistic jets with cylindrical topology like those associated with AGNs, some people further use this approximation for collimating relativistic outflows in the asymptotic domains from central sources. It is argued here that one can not collimate outflows by the FF magnetic field only, that is, the flow-field structure must asymptotically be conical far out from the light cylinder.