I have never lost a major piece of work to a crash, and I have written book-length documents in it. It has support for even longer works, running to multiple volumes. It has advanced capabilities for numbering independent sequences, equation editing and generating PDF versions of documents, and many other features to support a range of writing styles and document types. Another really good feature about FrameMaker is its cross-platform compatibility. It is available for Windows, Mac and a variety of UNIX variants, including Linux.
All versions use the same document formats, and it's possible to share documents without conversion.
Of course nothing is perfect. FrameMaker requires a lot of learning to use its more advanced features, and despite its professional focus, has some surprising omissions. If you change the global font size in LaTeX, paragraph indents etc. But in any case, the point is that Word, despite lacking much of the careful thought and design of FrameMaker, is just as large and complex. It is superficially easier to use, yet is harder to use to achieve some of the more sophisticated effects required for complex documents.