Mixing styles and direct formatting causes some of the biggest headaches in using Styles in Word by causing inconsistent and incoherent behaviour. Updating the style will inconsistently overwrite any direct formatting.
For example, a simple document with two styles: “Heading”, which is Helvetica size 12, and “Body” which is Times size 11. In the course of preparing the document, the writer decides to insert a quote and indents and italicises some Body text.
The writer does this manually, directly formatting the text. The document now has some paragraphs of “Body” without any direct formatting, and some other “Body” paragraphs that look quite different.
The writer now decides to change the font to Charter. Depending how this is done, all paragraph level direct formatting (such as indenting and italics) may be lost. Alternatively, the writer decides that italic Helvetica looks good, and decides to change the Body style to now be italic. Depending how this is done, it may cause the previously italicised text to stop being italic.
Expand this to working with a long, complex document with a heavy mix of styles and direct formatting, and it is disastrous.
Frustratingly, Word does essentially nothing to stop a user adding direct formatting to a styled document.
The exception – emphasis
The one exception to this is adding emphasis, though direct formatting to one or more words within a paragraph. Word tends to preserve this formatting without problem.