Redundancy is when you unnecessarily repeat yourself. Conciseness is when you’re not redundant. (Terseness is when you take out too many words) Good writing is concise. No unnecessary words. This applies to especially to expository writing. If you’re writing a love letter or a poem, it’s okay to not be concise. But when you want to explain something, be concise.
Here’s an example of not being concise:
The [watch and clock] tax was repealed after a campaign by the Clockmakers’ Company, and promptly replaced by Income Tax, which U.K. citizens still pay to this day.
You could write, “…which U.K. citizens still pay” or you could write, “which U.K. citizens pay to this day.” Both have exactly the same meaning, and each way of writing concisely has more punch than the original.
So write punchily!
PS—here’s a picture of a timepiece designed to minimize that tax.