Imagine this scenario:
You are on Twitter participating in a lovely group discussion when suddenly a well known agent that you have long admired chimes in and her comments add greatly to the discussion. The conversation continues for half an hour and you are so thrilled that you were able to converse with someone you admire so much.
A few days later you realize that that same agent is now following you and you are absolutely flabbergasted when she sends you a direct message telling you that she enjoyed your writing samples on your blog and is interested in seeing more of your work. She requests a partial manuscript.
Do you have something prepared ready to send? Have you prepared a query letter? Have you completed a revision of your first three chapters even though you aren't yet finished with your manuscript? Do you even have a short synopsis ready just in case?
No, you say. Neither did another unpublished author friend of mine. She had been told by other authors to complete the entire manuscript and finish revisions before even thinking about querying an agent; that her manuscript needed to be near perfect before submitting it. Needless to say she was very disappointed that she didn't have anything that she felt was good enough to submit at that time.
She didn't want to let this wonderful opportunity pass her by so she contacted the agent back and advised her of the situation and offered to send her a synopsis within the week. However, the agent refused the synopsis alone, but did invite her to submit it along with her first three completed and revised chapters as soon as they were ready.
Needless to say the author is thrilled at the open invitation, but is also very disappointed that she had nothing prepared to send the agent upon request. So now she is working frantically to revise the first three chapters and complete the synopsis so she can submit it as soon as possible. She is also much more dedicated to completing the manuscript now that an agent has shown an interest.
This just goes to show you that you never know when or where opportunities are going to come knocking and that we all need to have something prepared to submit just in case.