Below is a scan of a proof of some lines cast this past weekend for a friend. 8pt Linotype Paragon set on 23 pica line, regular justification. I let the space bands do their work, and wanted to learn their tolerances and get used to how a line would space out according to how many spaces bands were used vs. word size, etc. I figured this face could handle some "gappy" word spaces, but I was surprised at how this composition appears fairly consistent. Even though there are some lines with ambitious word spacing, none of them stand out as being too obnoxious with noticeable "holes" or "rivers" in the composition.
What I learned: generally speaking, space bands have a "spread" of 3 pts, so if you have at least 5 space bands in a line, they will easily take up a pica worth of space. I'll add a separate post which will describe the markings and different thickness of Linotype spacebands.
Another thing I was reminded of after setting these lines are the rules for indentation. For commercial work, the rule of thumb is to indent paragraphs by an em for lines set up to 20 picas. 1.5 ems for lines up to 25 picas, and 2 ems for lines above 25 picas. Of course depending on type size, leading, etc. there are exceptions. But after looking at the paragraphs I set below, I think my 2 em indentations are a bit too aggressive. I referenced the book "Linotype Keyboard Operation" for the refresher.
Oh, after clicking on this photo to take a closer look, I noticed something else. See the lower case "i" with a problem? I'll have to run the mats out and have a look at them.