  The physics of manganites appears to be dominated by phase competition among
ferromagnetic metallic and charge-ordered antiferromagnetic insulating states.
Previous investigations (Burgy {\it et al.}, Phys. Rev. Lett. {\bf 87}, 277202
(2001)) have shown that quenched disorder is important to smear the first-order
transition between those competing states, and induce nanoscale inhomogeneities
that produce the colossal magnetoresistance effect. Recent studies (Motome {\it
et al.} Phys. Rev. Lett. {\bf 91}, 167204 (2003)) have provided further
evidence that disorder is important in the manganite context, unveiling an
unexpected insulator-to-metal transition triggered by disorder in a one-orbital
model with cooperative phonons. In this paper, a qualitative explanation for
this effect is presented. It is argued that the transition occurs for disorder
in the form of local random energies. Acting over an insulating states made out
of a checkerboard arrangement of charge, with ``effective'' site energies
positive and negative, this form of disorder can produce lattice sites with an
effective energy near zero, favorable for the transport of charge. This
explanation is based on Monte Carlo simulations and the study of simplified toy
models, measuring the density-of-states, cluster conductances using the
Landauer formalism, and other observables. The applicability of these ideas to
real manganites is discussed.
