I've limited myself to using only the Pretty Print clean-source setting since it became an option, but even before that... I never ran into a situation where HTML Tidy (in Sigil) resulted in the "loss" of any well-formed, valid, ebook-typical xhtml. Yes, I realize it's still technically possible—and as such, may be considered too risky by some. That's understandable. But unless you're feeding it the most heinously formatted xhtml (or you just don't have the requisite knowledge/experience to directly edit xhtml correctly/safely), I don't think the HTML Tidy feature in Sigil is quite the evil bugbear that many seem to want to make it out to be.
If you don't need it; then by all means, don't use it (full-blown Tidy). But if your coding skills/knowledge dictate that you might need some "help" of the automagic variety?... well then, you generally takes what you gets. *shrugs*
Last edited by DiapDealer; 02-10-2013 at 09:25 AM.