Yes, this is just bad advice if your audience is fluent in mathematical notation.

There's another piece of advice that is bad for formal mathematical writing:

> And don’t use the same word repeatedly — it’s boring.

If the word has a formal definition, this is bad advice. For example, in a game theory setting, we might say there are n agents. If we start calling the agents players, people, etc., it can get confusing, especially if there are other entities involved besides the agents (such as a mechanism designer or so on).