What is the point in primary's

In the groups feature,

We can set a group as someone’s primary group.

What is the point in doing so?

One use I know is to assign group flair, if multiple groups have flairs configured, primary group takes precedence.

From trusty old ask.discourse:

:+1: Exactly why it is leveraged in this plugin, to provide a tailored homepage:

That should be removed if anyone can just change their group flair anytime

I think the key point here is “by default”, right?

did you try searching Meta first? because the first result explains it pretty clearly:

you have a well-established history of posting without reading. Discourse, and especially Meta, are designed for reading. you would do well for yourself to do more searching and reading before posting.