So there is a couple of things here..
Groups are just that Groups. There is no user in there just Groups and what each Group will have access to..
Where it matters is the Users tab. That is where you will have the name of the Users or admins.. Only access will be given to anyone in the Users area not the Groups area..
Can't delete groups as they are made by the programming of the recorder or camera manufacture. What you can do in the groups if you will not have any users is take away all rights to playback and leave right to see one camera that don't matter if any sees or just take all view rights either way it is up to you. What ever you change if you add normal user in the future you will have to give back access you want so it is an area that is setup to give out access to each type by default a set way without having to make loads of changes..

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This is only user I have on this machine other 2 above are just groups for when I add user as default settings they will get when added to that group

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Be Safe.