In consulting and in grad school, I edited a number of technical documents. One of the first things I looked for was abbreviation usage. I did this 1) because it’s a simple fix, and 2), because it’s frickin’ obvious, people!
When you’re writing about contamination, you often have a number of terms that you’d rather abbreviate, such as Super Complicated Organic Compounds (SCOCs). The first time you use an abbreviation like SCOC, you define it so that the reader knows what it is. Then, you don’t need to define it again. You do not randomly write Super Complicated Organic Compound (SCOC) when you start a new paragraph, or whenever you feel like you haven’t spelled it out in a while. You define it once.
If you’ve got a technical report of any length, such as a thesis, it is nice to have a separate list of acronyms/abbreviations right at the front for the reader’s reference. In the rush to finish my thesis, I didn’t get around to this. It’s one of the many small things that I would have fixed if I’d had another week to submit it.
A paper that has its abbreviations and full-length terms all mixed up just looks like a mess. When you’re trying to convince folks that your ideas are correct, you don’t want your readers to think, “if they can’t even get something stupid like abbreviations right, how much can I trust the rest of the work?”