I once watched a secretary correcting a document in a word processor; she was adding a word to the first line of a paragraph.
As she added the word, the last word on the line dropped to the next line, but it didn't flow into the rest of the paragraph. There was a hard return at the end of the line.
She put a hard return where the new line ending was and joined the word that had dropped to the next line. This forced the last word of that line to move down. She put a hard return where that line now ended and joined the word....
This continued to the end of the paragraph.
I am reminded of that incident whenever I see hard line endings on a web page, usually coded with <br>. They may work in the designer's browser, at the designer's font size, but their viewers may be using a different font size or a larger or smaller browser window. When that happens, the paragraph falls apart. Here are three examples I found:
Once the <br> tags are removed, the paragraphs appear as they should, and they will work no matter what font size the viewer has: