There's a space between the dot and the script name.
The dot is a shortcut for the "source" built-in command. "source" reads the commands in the shell script into the current shell and executes them. Executing a script directly (i.e., your option B) launches a separate instance of the shell, which then executes the script. In option "A", variables set by the script will persist in the current shell; in option "B", nothing that happens in the script will affect the current shell.
The "source" function is used a lot for things like picking up configuration data for use by a calling script - especially in places like the /etc/init.d scripts in Red Hat/Fedora Linux where they designed the system to separate the updateable script code from the user/system-specific data.
By using a sourced script instead of a config file, the calling script is relieved of the need to parse the configuration definitions and assigne them to working variables - the shell does it.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.
Don't get me started about those stupid light bulbs.