#!/bin/bash --login vs #!/bin/bash
The main difference is that a login shell executes your profile when it starts. From the man page:
When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.
When a login shell exits, bash reads and executes commands from the file ~/.bash_logout, if it exists.