What is the purpose of category store association in multistore?

[Multistore user]

Hello, I have three websites on Prestashop 1.7.7.2

We sell products from two brands. I have three stores in multistore, one B2B site with all the products and two B2C sites for the two brands (each containing only the products within that brand). Brand A and Brand B.

I gave the two groups of products different categories (A and B) and I used store association in the category admin to turn off the irrelevant category in each B2C store.

But all of the products are indexed in Brand A’s B2C store, all the products from both category A and B are available to be indexed by site search, Google and the XML site map (even though they are not accessible as the Brand B category is disabled in Brand A store).

It turns out that all of the products from the main trade store are published in both B2C stores. To unpublish them, I need to associate the Brand B category with the Brand A store otherwise the products for Brand B do not show up in the Brand A store admin to unpublish them there.

Is this expected behaviour for category store association in multistore?

I had hoped (expected) that disassociating the Brand B category from the Brand A store would remove all those products from the store but it does not (the product pages are still published and accessible by URL).

Am I right in thinking that category store association is more or less useless? (My stores are better if I ignore it)

Is there a good use for category store association in multistore?

(Please forgive my sketchy understanding of Prestashop, I am trying to understand the best way for me to use it to good effect in my stores)

Regards, Multi store user