I like to use HTML when adding content to the body of my nodes. I like to keep the HTML clean and uncluttered. I like HTML that has semantic meaning.
I indent using 2 spaces instead of a tab, which prevents having whitespace chaos. I indent using 2 spaces instead of 4, which makes it more compact and readable.
So I create nice, well formatted HTML, 2-space indent, save the node. Then when I come back to edit it, Drupal adds tabs whenever indent-spaces used to be and now it looks horrible and more difficult to read.
Also, Drupal removes the spaces between paragraphs that I add to make paragraph groups more readable.
How can I prevent Drupal 7 from adding whitespace to source code?
