Some comments are obviously left by bots. Someone paid a fee to have comments inserted into web pages that are related to a specific topic. it doesn't work, but people keep paying for it. usually, the grammar is atrocious and the content has nothing to to with the subject of the hub. These comments are always stunningly positive and never have anything specific to say. Those get deleted immediately.
I have several hubs on cheap designer watches and those hubs get spammed by bots all the time. Lately I have been deleting the comments and re-posting them, with links removed, under my name. That's a little fun.
Recently I asked permission to leave a link to one of my hubs in a comment I left on another hub. The link was germane to the hub I was reading. The writer politely declined my request because he/she wanted his/her readers to have 'exits' to his/her hubs and no one else's hubs.
Oh well. That's certainly his/her prerogative. I will allow other hubbers leave links in my hubs if the links are relative and the other hubber has a decent track record of writing. I do not allow links in comments when the other hubber obviously created his/her account simply for the purpose of plugging his/her other sites or products.
But that's just me.