How to use an indexer just for a specific profile

[TRaSH]

It’s not possible to specify which indexer is beeing used for a profile.

found a link with a little explaination when using google on reddit.
https://www.reddit.com/r/usenet/comments/2xvfis/what_are_categories_when_setting_up_an_indexer_in/

And some more info:

What happen if I don't select any category on Indexer?

In sonarr, when I add a Indexer I’ve to compile Categories filed, so I put all the category where I want to search. What happen if I don’t set any category number? Sonarr made a global search or what? In my mind If I search on whole site I can find unwanted results, so maybe is better use categories but sometimes, bad releaser, post their works in wrong categories. The main “problem” is that some traker have so many categories that is quite long select all categories, copy/paste … copy/paste…