Why do some websites use numbers next to filters?

I've noticed multiple apps/websites (especially travel) make use of putting a number next to a filter to indicate how many results will be returned.

I have some concepts of why this is a useful design pattern to a user (especially if users often obtain 0 results). Reducing the complexity of choices, visibility of system feedback if it updates CTA of applying filters, improving communication & trust...

I would like to understand if there is a more solid why to this design pattern, rather than an 'it just works' or 'other sites do it'.