[Hans]

By default every user has a web, in which they can upload data.
This can be very nice for FTP-purposes or when you want to switch over very fast to another website.
(The uploaded site of the user market as administrator, is visible from the Internet).

If you don't want webs for all the users, you have to modifiy the ISPConfig-database within PHPmyAdmin.

I would not do that if i was you.
By informing the users about the procedure, you can avoid mistakes.