Prepress shops and printers have this equipment by necessity, but charge accordingly. However, a good art director, working with a photographer ahead of time, may be able to plan a photo shoot in such a way so as to reduce the retouching that will be needed. But, since most photography from even the best studios usually requires some retouching, it's safer to budget for it than to ignore it. In multipage brochures or catalogs, this can be a time-consuming chore. In simple pieces, it is relatively easy and inexpensive.
Color is another matter again.
Color proofs are costly but necessary in order to see that the colors have been reproduced properly. Altering the copy or artwork at this stage gets expensive because you are already into the photographic process. If you are working in color, it may be necessary to pull new film for each of the four process colors. Copy changes may be simpler if the copy is clear of any background, but that is not always the case. Budget for some alterations and hope you don't need to spend the money.