Newspaper advertisements was where I began in artwork and design, making ads for Rover, BMW and Mini. (Was that really 20 years ago?! Yes, indeed it was!) I made Call-Offs for the car dealerships, and I averaged about 30 or 40 a day when it was quiet, and over a hundred a day when a new car was launched. It taught me a lot, about being efficient, using style sheets and not cluttering up pages with guides, but instead using the X and Y co-ordinates. I'm glad I learnt all the disciplines that my Call-Off days taught me, because it set up my working habits which I still use today. By being accurate from the start of a job, less can go wrong.
I like all my layers labelled and organised, cutters and printers marks kept seperately. Same with style sheets, spot colours and images etc. I like clean artwork, nothing in any palette that isn’t being used – or at least I keep those items in a folder marked as such – if keeping for future versions. With CC libraries and the ability to easily append common elements, it's easy to pop them back in the artwork, so if it isn’t being used, I think it’s preferable to clear it out!