to think Twitter should add 'Monitors' as a category as well as 'followers'

[Orlantina]

Because followers implies that you are a 'believer' in what they say as opposed to 'monitor' which means you are just seeing what they say.

Then people can't just say they have 10 million followers. They may have 2 million followers and 8 million monitors (yes, Trump, that means you)

(shamelessly nicked from The Now show)

If you just want to read someone's tweets easily without having to follow them you put them on a list (which can be public or private)
I never read my timeline, only my lists (mostly containing people I do follow, but some whose tweets I just want to see (Donald Trump is one of them)