In general terms, if I comment on a question or an answer to that question, I am interested in that topic.
However, I get notified if someone comments on the original question after me, but not if someone answers the question after me.
If I have responded to a particularly 'hot' topic, I can receive multiple emails informing me of the responses, looks like spam mail.
Two suggestions -
1) Notifications of any responses to the question, either comments or answers.
2) Restrict notifications to one per topic, until the notification is acted upon.
This would allow topics to be followed in full, but reduce the number of notifications received.
Example of email response from another forum -
A reply has been posted to a topic you are watching by xyz.
View the reply at:(link given)
Unsubscribe to this topic by using this link: (link given)
More replies may be posted, but you won't receive any more notifications until you read the topic.