Using a directory-based bash history allows for a record of shell actions on a directory basis, so a group of developers have some record of what was done while in a directory, when, and by whom. This can be helpful when trying to reconstruct history with limited documentation.
I know this setup will be of some benefit to my successor at my previous job because he has access to everything I ever did in any project directory.
Place this code in your ~/.bash_profile or ~/.bashrc
(type source ~/.bash_profile (or .bashrc) to load this for your current session)