Re: Why choose plain text over HTML email?
Two other things on the so-called bandwidth issue.
1) Depending on one's group settings, email is by default on groups.io sent as multipart/alternative per section 7.2.3 of RFC 1341. This means that everyone downloads both the text/plain and the text/html versions of the email and the MUA picks the one the reader selected in preferences. That means that if one was using text/plain to reduce bandwidth, that's not going to work for those groups.
2) While it is true that HTML encoding makes the size of the message larger than plain text, the difference is vanishingly small compared to a single image or attachment, which is orders of magnitude larger than the difference. When all is said and done, HTML is still text, still ASCII characters. <bold>foo</bold> adds the cost of exactly 13 characters over just typing the word 'foo'. And, as Chris points out, overquoting is also a huge consumer of bandwidth, much greater (especially for long threads) than the number of characters used for HTML tags.
P.S. For the plain text folks, I italicized the word "both" in the second paragraph above. The typing of this P.S. also consumed more bandwidth than the HTML tags used to create that font style.
P.P.S. I included a link in that same paragraph to the RFC as a method of citation to back up what I was saying. I consider this a best practice in discourse and there is nothing dangerous about it.
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