Once upon a time:

From Charles Reich's memories of his 1950's law work:

[What] I remember best was proofreading. Stock and bond certificates had to be perfect. Much of their text was printed in tiny type. Often the printing was on a tight schedule and had to be completed at Ad Press late at night.

The proofreader's job was a serious responsibility. No one was too high up for this task. Mr. Swatland seemed to relish doing this himself before any document left the office, no matter how many other lawyers had already given their approval. For the associates, proofreading was a two-person job, with one reading aloud every syllable, capital letter and punctuation mark, so that the reading sounded like a special language: "This Debenture, two initial caps, com," and so forth.

I remember this as well. When you don't have word processing equipment that channels your writing into patterns and formats, when you have to deal with carbon paper for copies and white out for corrections, when you don't have a spellchecker, and when you have to retype each version from scratch, proofing becomes a priority.