i'm sure this is documented somewhere but i can't seem to find exactly what i'm looking for. slackware creates a huge list of groups by default. i'm wondering where i can find out the purpose for each of these groups and which ones are safe to delete.

A layman's point of view to be sure, but consider everything that happens in Linux has to have some permission behind it. Each of those oddball groups exists so various drivers and services can perform their duties unassisted. That is they have pemissions partly by being assigned to one of these groups, and they don't have to wait for 'root' to tell them to go to work. I am willing to bet that there is at least one program, library, driver, or what have you, if not hundreds that can lay claim to any one of those groups, as obsure they might seem. Just defining them doesn't take more than a kilobyte of disc space. I would certainly NOT remove them.

If you want to check if any files are owned by a group, run:
This will catch most groups that are in use. There are a few exceptions to this:
1) Files that udev dynamically creates in /dev. (The groups tty and usb are two examples of this)
2) Programs that drop privileges during runtime. Some programs may fail if they try to switch their effective group id from root to a group that does not exist.

Because of the above cases, it is often risky to remove groups (and they don't do any damage being on the system even if they are not used).

If you are thinking that the long list of groups might obscure an account made by a virus or hacker, then a program such as rkhunter can alert you of any changes to the user/group list.