What are film treatments for?

I have spent the last two days working on two versions of the Memorabilia treatment (formally known as the OTHER treatment!) The process has made me focus on the fundamental purpose of treatments.

Just so we all understand each other, by 'treatment' I am talking about a document which conveys the movie in prose. It typically reads rather like a short story and is usually written in the present tense. There is significant variation in what different people expect from a treatment, but this is my simplistic take on it.

Having said the above - what is a treatment actually for? I don't know about other people, but for me treatments fall into two distinct classes.

The first kind of treatment is a document written as a precursor to writing the screenplay itself. It is a form convenient to work with, readable, comparatively short and easy to navigate. Writing a screenplay from this kind of document would be a comparatively simple task. In the extreme case, it would only require reformatting.

The second kind of treatment is a document designed to get other people interested in the project. It could be produced before the screenplay is written or after it. Either way, it is short, simple and readable enough to tempt a busy person. Its job is to generate an emotional response in the reader.

We have been working on the first kind of treatment for Memorabilia for several months. Each reworking has improved the document. And we stand almost ready to launch into screenplay writing.

Only today have I started to produce the second kind of treatment for Memorabilia.