While the options to upload an image or selecting an ImageCache preset, etc. are useful in general, in some cases it makes sense to hide them (set defaults before that) in order not to confuse inexperienced users. Consider my case:

I want to buld a community web site where users can upload images into their own galleries and later on insert some of these images into articles they can also write. I also want that to happen in controlled manner:
1. Users can insert images from their ALREADY created galleries, so there is no need for the "Upload" button on the ImageField Assist dialog. An option to hide this button should exist.
2. I need my users to be able to browse only through their own galleries for images to insert. That can be done by adding Views support to the dialog: http://drupal.org/node/613968
3. I have a predefined ImageCache preset and I want ALL images inserted into articles to use that. So I need the ability to select a default preset and then hide that option from my users. In fact I cannot expect my users to know what ImageCache means.
4. Same for the "Link" option - ability to be hidden
5. Same for Lightbox2 - ability to select a default and then hide the option
6. Same for Insert mode...

Thanks!