Reasons to use safe mode

Hello all I'm working for an ISP and I'm currently preparing to give users the possibilities to write and upload PHP scripts themselves. We are using PHP 4.00. I'd like to hear what is exactly the reason to use safe mode in an environment, where php scripts are only executed by the webserver (apache module) and not directly through the 'php' executable. My basic idea is, that every user, which writes php scripts, is caged into its own home directory, and so doesn't have access to anything which is located outside. The configuration parameter 'open_basedir' does this job well (at least I got the impression). I'm currently trying to find out, what would happen if I would disable safe mode, while keeping the open_basedir variable to point to the users home directory. What sort of misuses/attacks are thinkable in such an environment? My main problem with the safe mode is, that the users can not write any files with php, even not into their own directory tree. Except if the scripts are chowned to the apache user, but this is not a real option, because the rights of the scripts are set to the FTP user after every re-upload. By disabling safe mode I could set up a tmp directory belonging to the apache user, where the users could write their files to. Additionally file upload could be made working much easier. Thanks for any comment (please write to sjo@spin.ch) Sam Jordan