I have used that in a project of my own[0] for convenience (avoid duplicated code), but it is uncommon, yes.

I truly think it should be avoided in general, especially when what you actually want (in OP’s article) is a config file.

[0] https://github.com/Frizlab/frizlabs-conf/blob/44030f4123e683... (w/ that, also see the aliases in the folder of the script)