The way VBulletin is set up, you can choose how to handle it yourself. Go to user CP and pick “edit options” – you can choose whether or not to subscribe automatically, and if you do subscribe, whether to get email updates or not, and if you do get updates, how often.
If you’re not an automatic subscriber, you can subscribe to any particular thread – with or without posting in it – by clicking on the “thread tools” dropdown.
Me, I’m a “few subs, no notifications” kinda gal …
If you’re getting deluged with emails, you could change your notification setting from “instant” to “daily” – depending on how active the thread is, that could cut it down significantly.