I suggest a new xml file type in the Open Document File Format family, which
allows us to save a part of a document(presently saved as *.odt). I mean that it
won't contain page settings and any other default setting(i.e. any setting of
font, margins etc. which weren't been configured by the user). My idea is that
we could save a useful sentense, a box with an explanation of a topic, a
complete table of a statistic etc. into separate files. Then we could paste them
directly into a new document.

An example:

1. While I'm writng a report with OpenOffice.org Writer about opensource
applications, I make a diagram about how many people in the world use
OpenOffice.org, I add a table with exact number of users by occupation and put
them in a box with the title "How many people use OpenOffice.org?". I save it as
"Open Document Partial Text"(I call it like that for the present). The file
doesn't consume much memory, because it contains only settings which I
configured specially for this part.
2. Some days later, I write a report about how people in the world save money by
using free stuffs. At the section "software", I simply click
menu->Paste->File... and paste the "Partial document" I made for the last report
about opensource applications. I don't need to change anything, because the
default settings are applied automatically.

So, the benefits would be:
* small file size and speedy operations
* no manual formal customizations needed