To unravel the role of doping in iron-based superconductors, we investigated the in-plane resistivity of BaFe(2)As(2) doped at one of the three different lattice sites, Ba(Fe(1-x)Co(x))(2)As(2), BaFe(2)(As(1-x)P(x))(2), and Ba(1-x)K(x)Fe(2)As(2), focusing on the doping effect in the low-temperature antiferromagnetic/orthorhombic (AFO) phase. A major role of doping in the high-temperature paramagnetic/tetragonal (PT) phase is known to change the Fermi surface by supplying charge carriers or exerting chemical pressure. In the AFO phase, we found a clear correlation between the magnitude of the residual resistivity and the resistivity anisotropy. This indicates that the resistivity anisotropy originates from anisotropic impurity scattering due to dopant atoms. The magnitude of the residual resistivity was also found to be a parameter controlling the suppression rate of the AFO ordering temperature. Therefore, the dominant role of doping in the AFO phase is to introduce disorder to the system, distinct from that in the PT phase.