If you’re writing a book, or a letter, and you want every paragraph to have the same amount of blank space after it, then I agree that yours is the way to go.
But I often work on graphics things where each page needs to have certain things on it, and in certain locations. That requires me to fine-tune the space between paragraphs A-B differently than paragraphs B-C. I certainly could use the Paragraph Formatting dialog box to make changes in the “Spacing After” section, but that is very tedious. I find it much easier to use “Spacing After = 0” for everything, and then have an empty paragraph between the two real paragraphs. This allows me to easily select the empty paragraph, and then make it larger or smaller by changing the font size. I can do this most easily with ctrl-[ or ctrl-], but even changing the font size in the toolbar is easier than going to the Paragraph Formatting dialog box.
In general, I prefer WYSIWYG over hiding the format info in sneaky places. So when I turn on the “show paragraph marks” (you know, that button with the left-facing “P”) I want it to show me as much as it can. With my procedure, I see that left-facing P for each empty paragraph, and its size corresponds to the empty space. But with your procedure, I have no way to know why these two paragraphs are so far apart, or so close together. It might be because of the “Spacing After” setting, but it could just as easily be the “Spacing Before” setting of the next paragraph.
(Colophon, I probably went into more detail than you personally needed to understand me. I did it for the benefit of other readers.)