The annoying thing about Fossil is that it doesn't let you squash commits, not even in your private branches - they have some kind of philosophical point about that.
If you happen to agree with it, then yeah, it's great. If you like to commit quick and dirty and then tidy it up by squashing into logically complete and self-consistent commits, too bad.
I can certainly see the appeal of having neat commits but I tend not to worry about them. On a couple of occasions, with my university writing, having a immutable history helped me figure out, for example, how something had ended up in a final draft without citation. I'd deleted the citation which was a quick URL paste in a comment block in an earlier draft, and I'd never saved it to zotero. If I'd been able to tidy up my commits I'd likely have lost it completely.
The appeal depends on how messy your commits are to begin with. When you know that commit history can be rewritten later, it suddenly becomes okay to commit incomplete code that doesn't properly run or even build, effectively using git as an undo system with branching. But the resulting history is completely unsuitable for any future attempt to use `git blame` and such.
