A
pseudogene is generally not functional, since it lacks the
promoter at the beginning, or since it is inserted in a region of the
genome which is not
transcribed. This is still "useful" in
evolutionary terms, since it might be reactivated after some
mutations occur. This (both with and without reactivation) is the evolutionary cause of
homologous genes.
Some pseudogenes are, however, completely "useless" in this sense -- see processed pseudogene.