Text styles are one of the most important features in Scribus. Using text styles will make text handling and formatting much more easier. As they are a way to reproduce formatting all over the document, you'll get many benefits from them, such as:
There is no need to remember what the font size, color, or kerning you put on a title or so; styles do it for you
A bunch of text properties can be applied at once quickly in a single click
The overall aspect of your document can be easily modified if you change your mind
Access to some new features such as Drop Caps and language settings (for check spelling in a multi-language document)
A bunch of font defined properties can be shared throughout several documents
There is no need to care anymore about the lack of a text undo engine in Scribus
We should find some other benefits, but using styles is like using master page. Once you're used to them you can't go back: they are easy to define, easy to apply, easy to change, and divide the working...