From most viewpoints, text objects are no different from any other object type; you can not only transform but also style (choose fill or stroke, adjust opacity, apply filters, etc.) a text object as a whole without even going into the Text tool (and, of course, without losing the ability to edit the text). However, only the Text tool allows you to change style properties specific to text (such as font family and font size) as well as apply style to spans (fragments) of a text in an object.
To have a different style, a span of text must be enclosed within a
span element. You don’t need to think about it, of course; for any overlapping or nested spans you create or delete, Inkscape manages the
span elements automatically.