Why should you be reluctant to assign permissions to the group everyone for most files?
What did you mean by assign permissions? Did you mean about the windows file sharing? Sharing files and folders in your local network can be the easiest and fastest way of sharing your files however, this comes with unsafe situations. When you share your files no passwords will be needed to access from your computer. To free yourself from the danger of stolen files, after sharing the files and your colleagues/someone you know already got the file always disable the sharing. Do not enable file sharing when nobody needs to access from your file. If you're not in a hurry use an external disc to copy your file and give it to someone who needed the file rather than enabling file sharing.
Permissions are an important issue for any group work. There may be ignorant people / users who do not know much about the work. They might modify same important files that may damage your team work. All the group members have permission to files as they are assigned by the administrator. Mostly A group contains members where works are similar enough to be given same permissions to all. The utility is that you can have a control on all the members just using the group permission changing which change for all the members.
In linux you will find “chmod” as the command to change permissions for the group, user & others.
chmod 777 means all have all permissions.