Long format is essentially the same as wide format, except that it gives each prompt in a session its own row, and provides more detailed information about each prompt. This additional information includes prompt response lapse, the prompt text, and whether or not the mobile user responded.
Further, long format is not set up for multilevel modeling, like wide format is.
For more information about the differences between long and wide format, please see this article.
The use of the terms long and wide format differ slightly from longitudinal studies. For more information, please see this article.