I'm not hot for reimplementing printf, but I did need an interface that made it easy to print diagnostics for various objects; rendering them to the stack and then passing them to the underlying printf implementation makes for a lot of boilerplate code.

In addition to reducing boilerplate and aiding portability, having our own printf implementation aids in consistent behavior across platforms, and allows for a deeper integration with our streams and buffers so that we don't need to make a series of clunky calls to measure how much storage is needed before passing the formatted data into the lower layers.