This command will set all users+v when they enter the room unless they are already being opped. Because the VOP list cannot accept open hostmasks like *@* you would use this command to give voice to all users. They will be voiced in the room and able to look at the room lists, but they will not be able to invite themselves into the room. If you ban them, they can revoice themselves and still talk, but if you kick them out then they cannot rejoin.
Example:
/msg chanserv set #spiderslair autovop on
This command is generally not useful. It will require anyone who causes problems to be banned and kicked, since they will be able to revoice themselves and speak through bans. It also makes your UOP/VOP/AOP/SOP/AKICK lists public to everyone on the network. However, if you want your lists to be public, or have a reason to voice everyone, this will let you.