Please Don't Make Spreadsheets Pretty
I have come across my fair share of spreadsheets; they are almost always Excels, because that is what everyone uses. I don't dislike using Excel. It's a fine tool, even though Microsoft till this day still insists on keeping its non-standard copy-and-paste operations that tripped me multiple times.
What I really dislike is the way some people 'decorate' their spreadsheets with boxes and arrows and colors and extra text and all sort of nonsenses that make using and manipulating the data difficult for me. Just like Dr Drang observed, life gets more complicated when I cannot simply export the data to a CSV file and run them past some of my PHP scripts.
Microsoft Word, technically, allowed users to separate out the presentation from the 'data'. (Yes, most people probably don't use that because it is complicated.) I am not sure if there are similar features for Excel, but I haven't seen it.
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Link: My Rules for Using Spreadsheets, by Dr. Drang, And Now It's All This.