In excitation transfer, energy must be considered delocalized unless the presence of specific localizing processes is demonstrated. A criterion for localizing processes is given. On the basis of this criterion, it is found that, for weak interactions, localizing processes in liquid solutions at room temperature are unlikely. Localized and delocalized pictures give equivalent ensemble averages in the incoherent limit. Since this limit cannot be reached in the presence of resonance interactions, the equivalence is only approximate, and only the delocalized picture is generally valid.