You haven't linked to any specific tutorials making this recommendation, so it is hard to know why specifically they recommend it, or for what kind of development, you're setting your Mac up.
I have seen many development-oriented tutorials recommend that you setup a secondary Terminal that is run under Rosetta as a convenience. I.e. you duplicate your favorite Terminal program in /Applications, and set one to run under Rosetta and the other to run natively.
This makes it possible to use the special Rosetta Terminal and be sure that programs you run in there will be run through Rosetta without you having to explicitly ask for it. If you often use a program or programs that require this, it can be easier to do it like that.
If you only have a single program that needs special treatment, it might be easier to simple setup an alias in your shell to run that program in a different manner than the rest. YMMV.
In terms of your long list of questions:
Problem it addresses: Avoids having to manually ask for Rosetta when needed. Disadvantage: Won't get native performance when available.
What software needs it: None. You can just use a regular Terminal and ask for Rosetta when needed.
Is it an outdated recommendation: Perhaps - impossible to know without knowing specifically what you're referring to. If it was recommended due to some often used programs not being available natively, and they still aren't - then no it is not outdated.
Is there a way to track across multiple packages whether this step is necessary: The step is never necessary.