I remember giving some artwork to a mailing house. It was a very simple thing to print, 1 colour over 1 very few copies to send with a mailing. The mailing guy tried to sound really in the know about printing. I asked him if he needed crop marks and he said that he did.
He was then asked to bring a print out here by someone else. The guy at the mailing house came and brought the printout. I didn't know he was here yet. The guy who asked for the printout stormed into my office all upset and said, "What are these things on the corners of the print out and why did the artwork shrink down?"
I looked at it and I smiled. I understood that the guy at the mailing house didn't know what he was talking about, and he definitely did not need the crop marks, instead he printed them into the sheet of paper and had to shrink the artwork to make it fit into the sheet.
So I said to the person who wanted the print-out, "I get it, I'll give them another one without the marks. The mailing house guy said to me that he wanted them." The reply was, "Why don't you go and speak to him and ask him what these are?". Me: "I know what they are, they are crop marks. They are used by printers to cut paper to size (I gave a lenghty explanation on how crop marks work)". So I got in answer: "Why do you modify the artowork? I didn't want those marks!" Me: "I didn't MODIFY the artwork. That's the way printers do it, they are not supposed to be printed and the mailing house guy said he wanted them!" Other person, "Stop acting as the one who knows everything!" Me: "Look, I KNOW what I am doing. I know how to solve the problem, it's no big deal, so what's YOUR problem, hey?"
Eventually I just provided the new artwork without crop marks. I couldn't believe how the other person, who was completely ignorant of pre-press, was getting uptight with me because "I changed the artwork!"