(http://irclogs.wildfiregames.com/2019-09/2019-09-02-QuakeNet-%230ad-dev.log)

I didn't say "purposeless", but I tried to discover the reasons (use cases) why it was added, and the unreported use cases which might have ocurred and then the implications on the code if one was to consider use cases.
Yeah deleting it is an option. But I can't say with certainty without having worked with the code more closely myself, which is why I asked about that.
It seems there are use cases for multiple user configs (multiple users, multiple passwords, multiple hotkeys for instance), and there may be use cases conceived for system-wide config changes. I don't know about that. I'm not raising a concern unless there is something broken which is often discovered aposteriori when users run the administered code.

I guess most features are features that one user uses, you mean I'm the only one? I don't know, perhaps, I didn't survey. If there is a valid use case for the file then perhaps more people use it. Perhaps (actually certainly) it's advertized to the general user to use local.cfg and that's one part that should be changed if the file is removed.

(Hint ^)

Now where I look at my local.cfg and user.cfg, I remember one of the technical differences which are an unconsidered but perhaps considerable use case: code comments. local.cfg allows them, but user.cfg doesnt really support them because each time the game saves a config it overwrites the file without comments. I mentioned that one too on IRC, and I guess that 'feature' may still be dropped, if one wanted to, but one would have to drop it consciously and then under balance of pros and cons.

Another difference is that user.cfg is written in alphabetic order, local.cfg is written in the order specified by the text editor.

So it means the use case of saving per-user config values is covered by both local.cfg and user.cfg, therefore that use case does not grant reason for local.cfg's existence. And the other difference between user.cfg and local.cfg is allowing the user to store user config options with a text editor with code comments and arbitrary sorting order, which may be dropped if the author, reviewer and the users agree.

Deleting local.cfg will make it impossible to keep config options commented and semantically grouped.

Then again the part of grouping config options semantically is probably better fixed by providing categories to the options, for example renaming shadowquality to graphics.shadowquality would mean that its grouped with the other graphic options if sorted alphabetically.

So it's probably ok to delete it and probably ok to keep it and also ok to create a multi-user config system and also probably ok to support comments etc. My actual questions are actually not answered, then again asking questions is not wanted by the community because it's time consuming (unfortunately it's necessary if one doesn't want to break stuff unintentionally).

I wonder only about which parts of the code were accepted.
I can adapt to a removed local.cfg.
It requires a survey to make a statement about the number of users of a given feature, but it doesn't require a survey to decide which features are superfluous.
The hint was about the wiki pages that recommend the player to use local.cfg.