The .bash_profile, .bashrc, and .profile files all link to the same shell-startup file. This setup was chosen for a few reasons:

• It simplifies the process of figuring out which file is loaded when. Instead of having to trace through multiple files, there's just one central file to look at.
• The various startup files sourced during startup are required to perform whatever tasks are needed for that file. These tasks are usually broken up into discrete functions. For example, shell_startup.d/tmux sets up the environment for use with tmux.
• This setup also ensures that aliases and other configurations work when shelling from vim, which is a common use case.

This setup has been found to work well, but as with any configuration, it may not be suitable for all use cases or environments.