  It is shown that for materials near the metal insulator transition, inelastic
losses can give rise to substantial changes on a scale of 10-100 meV in the
observed lineshape compared to the intrinsic spectral function of an electron
photoemitted from a solid. These changes arise from the frequency dependence of
the loss function, similar to those directly observed in electron energy loss
experiments. For good metals and insulators, on the other hand, the inelastic
losses not important. We derive quantitative conditions to delineate the
various cases. We find in particular that La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ does
not satisfy these conditions, so that no significant losses are to be expected
in this material. This contradicts the reasoning of Schulte {\it et.al} [Phys.
Rev. B {\bf 63}, 165429 (2001)], who, on finding no significant lineshape
effects in this material, concluded that inelastic losses are always
unimportant.

Strongly Correlated Electrons