GIMP is a great image editing application, but its Text Tool really is not designed for working with text in a significant way. This shouldn't be a surprise as it isn't intended to be used to edit large blocks of text, unlike a DTP application like Scribus or even the vector line drawing app Inkscape. However some users are most comfortable working with GIMP and if you're one of these, GIMP's Text Tool does offer a reasonable degree of control for working with text and allowing you to fine tune the appearance.
If you're going to be working on projects that regularly involve setting even moderate amounts of text, I would strongly advise that you spend some time learning to work with Scribus or Inkscape, however if GIMP is your favored tool and you only occasionally work with text, then GIMP's Text Tool may be sufficient for your needs.
For instance, setting a little bit of text on a single side promotional leaflet could be handled reasonably well in GIMP. While GIMP doesn't offer particularly fine tuned controls for making targeted adjustments to text, the universal adjustments that are available do offer a reasonable degree of control over multiple lines of text.

