You will need both on MSI systems.
Most MSI systems, including HPC clusters: only $HOME/.bash_profile is sourced by default on login. To guarantee .bashrc is also sourced we recommend following this FAQ.
Non-HPC systems (e.g., Lab workstations and queue, login.msi.umn.edu, etc): both $HOME/.bashrc and $HOME/.bash_profile are sourced on login. See recommended setup methods below.
Inside NICE sessions: Only $HOME/.bashrc is sourced by default. Again, follow the recommended solution below to merge old .bashrc and .bash_profile files into one .bashrc.