I've read a couple of success stories of writers picked up by publishers only for a partial and a very detailed outline of the rest. So how can you send your manuscript if it's only a partial? And what do you need to know when picking up an agent if you only have half of the manuscript completed? I know very well the chances are minimal, but lady luck might smile on you, you never know.
If you have a very detailed outline, why not just write the rest of it? I mean, if the partial is exceptional it might fly, I just don't understand why you would risk it...what's the point? You still need to write the rest at some point, why not do it before you send it. Chances are your MSS isn't as good as you think it is and they'll see the partial, read a few sentences and throw it away...
It's not good enough for a partial, I'm just wondering how some managed to get it shopped as a partial when the golden rule regarding on how to get an agent is to finish off the manuscript.
There are always exceptions to rules. Just bear in mind that the amount of authors who manage to sell a partial manuscript are dwarfed by the amount who don't.
If you're talking about nonfiction, then yes, some writers get book deals based on a query, a detailed proposal and (usually) a couple of sample chapters. But most of these writers already have publishing credits in various media. They have a body of work to illustrate their ability to string words together. It doesn't work quite the same way in fiction. Getting 10 short stories published doesn't automatically prove you have what it takes to hold a reader's interest for 90,000 words. First-time novelists pretty much have to shop a finished product. It's the only way to show a publisher (or agent) that you've got the goods. When your first and subsequent novels sell well, then you might be among those who can sell future books based on an idea and a promised delivery date.