Modgits are best used when authors have a large amount of content that all needs the same display. In tools that lack modgits, authors need to either write code in the tool's language to simulate modgit-like behavior or individually author each instance of the model-object's interface. When there are hundreds of such data objects (such as questions and answers in an ASK system or points that follow up all those answers), individual authoring is fairly impractical, and we are failing on our ``usable by non-programmers'' metric if authors have to write modgit code themselves.
The challenge in writing a good modgit comes from making sure the modgit allows enough flexibility to fit with authors' artistic needs. If it isn't flexible enough, authors will look to other less restrictive tools. For example, question-viewer modgits took several months to refine to the point where authors could comfortably use them in any circumstance. At first they only allowed for one type of button, a workhorse standard Macintosh interface button. Authors wanted to put their own button art in their demos, so we added new types of available buttons with the ability to switch back and forth between Macintosh buttons and custom-art buttons. Along with just putting in new pictures, authors also wanted to edit the buttons' font, margins of text, and spacing between them. Finally, authors wanted controls such as buttons to make the question-viewers ``scroll'' (i.e., make more buttons available than can fit on screen).
By developing the modgits in parallel with authors using INDIE, we have a fairly comprehensive set of attributes for most of our modgits. For example, answer-viewer modgits have over twenty different attribute variables that can be set to accommodate all the different ways authors have wanted them to look.