I also agree with what you said. Keeping in contact with clients and being aggressive in that manner is not only smart, but necessary. But when referring to prospective clients there is a fine line between "pursing" these people and merely providing them information they may need, which can open the door to further conversations. I think some agents may tend to be too aggressive in the sense that they do not leave the prospective customer alone, which can have the opposite result of what was intended! As you said, an agent needs to know when to back off.
I have found out if I do not keep in good contact with my clients they WILL go on to the next agent.
It's when the client has made it clear through actions or words that they are no longer interested that you should back off. Even then make a follow up call in 30 days,you may reconnect and make a sale!
please see my blog that was written in a related subject to your question.