Invisible fields are useful when you have a particular field that is being automatically filled out by DBMan and you don't want people changing it. Invisible fields are achieved by using the input type "hidden" form element.
For example if you have a "username" field which is automatically filled in using the username of the person logged in, you probobly would not want this changed, especially in a "modify own records" environment.
I tend to keep my "ID" field (auto-incrementing numer) hidden, primarily so it can't be changed, but also because it isn't that important and the users don't need to worry about it.
Cheers,
- Mark
Astro-Boy!!
http://www.zip.com.au/~astroboy/