Trunking means that you have several resources, either frequencies or time slots, to dispatch out to conversations.
But you probably ask for the difference between One Frequency System and a conventional frequency.
You can specify talk groups and specify parameters for them like delay and alerts and avoids and other stuff for One Frequency Systems that you cannot do to a conventional channel.
I find it easier to use One Frequency Systems as I can enter several frequencies there and keep them in more manageble groups, addition to the more flexible programming of talk groups.
/Ubbe