Email uses 'failobj' instead of 'default'. I find that kind of odd, but oh well.
I'm not sure how useful a single data point is, but just last month I wrote an application that uses the DEFAULT section. Each configfile section gives a set of parameters describing certain attributes of an input file, and the DEFAULT section gives the default values for each of those parameters. A few years ago I had an application that made heavy use of interpolation and provided for config files that would override 'earlier' config files, and I used the 'defaults' parameter to the constructor to achieve this easily. I'm pretty sure I also added a few defaults programatically, but the memory is a bit hazy (I no longer maintain that application and I don't think it is in use any longer).