WordPress 2.0 introduced a lot of additional features in the Write Post screen.
One was the Post Preview sceen which now loads the entire post as if it would look on your site and this is a major bandwidth hog.
Few other things that you may want to remove are the Optional Excerpt, Trackbacks and Custom Fields and Post Author if you never use these.
Mark Jaquith‘s Clutter Free WordPress Plugin lets you hide everything but the post preview.
I like Mark’s plugin because it gives you an easy way to hide the things you don’t want and thus save space. However, it uses CSS to hide and doesn’t prevent their downloading.
If you are comfortable editting WordPress Core code, 24FightingChickens suggests a method to remove the Post Preview. It suggests using simple HTML Comment to prevent this display. Using the HTML comment tells the browser not to parse and display the text.
You can extend this even further to hide other things on the WordPress Post Screen.
I’ve written a short guide on how you go about doing this.
Read Cleaning Up the WordPress Post Screen.