I don’t care for automatic hyphenation in ebooks. The devices are pretty dumb and because they use an algorithm instead of an English major’s sensibilities, we get words like “mi- nute” instead of “min-ute” or “alt-hough” instead of “al-though.” While it is possible to turn on hyphenation for Kindle books, I’d rather not.
But. If a word has too many characters to fit on one line, this is what you get:
Just like an oversized image, characters disappear off the screen. Because there are so many Kindle devices and apps, you have no idea what settings or screen size your reader might be using. Judicious use of soft hyphenation is an easy fix to an annoying problem.
Here is the same text, hyphenated, at various settings on the Kindle Previewer:
If you’re building a non-fiction ebook, especially one with many long terms (technical or medical) inserting soft hyphens can prevent those unsightly gaps when a long word/term is jumped to the next page.