I change permissions all the time on our work NT4 Server, but only for my (or others) data files. Unless I know what I am doing, I will not change the permissions on system, system related or programme files.
Why do I change permissions, to helpsecure (or unsecure) the files so mishaps will not ocurr, such as others deleting or changing your files.
Also you must have been granted the rights to change file permissions by the file owner or the network administrators.
Gotcha's - nothing that a system administrator (or at worst a restore of the file from the system backups) cannot fix. I have locked myself out of files in the early days by giving someone else permissions over my own files.
I have used WinNT4 and Win2000 to change permissions.
Hope this helps.