Global functions are available across all your bots in your account, but managed from 1 single point. This enables you to create re-usable components that can be re-uses across your bots. See the global functions as templates, that are maintained as 1 object.
The global toggle next to variables and objects, or in functions enables the object/function to become available for all bots on the platform. Once a function, variable, object or sub is global it cannot be un-toggled. If you wish to remove the global setting, you need to delete the variable, function or sub first and add it afterwards again in the desired bot.