I have asked myself that question many times. I don't have much experience with repeaters or licensing, so I have always wondered at which point do I need a repeater license?
I'm no expert or bush lawyer but I did get an authoritative answer today by talking to the WIA: Anyone operating a transmitter unattended requires a repeater license.
Whilst there may be some discussion about wether this is the right or not (in a legal sense), the WIA advised that ACMA views unattended transmissions from an Amateur station as a violation of the LCD as such transmissions require a repeater license. Someone with time and money on their hands may choose to argue this case in court, but for the rest of us a repeater license solves the problem.
Looking at the Amateur License Determination (LCD) - section 9 states:Control of equipment at an amateur station
The licensee must ensure that an amateur station is operated at all times by a qualified operator or qualified person in attendance at the amateur station unless the station is an amateur repeater station ...
Operate means .... a station which receives signals through a public telecommunications network from a second amateur station and automatically retransmits those signals by radio
I believe that section causes the problem.
I could not find any reference to output power, so theoretically a 10mW DVAP which retransmits while the qualified operator is not in "attendance" (no definition found in the LCD) would violate the LCD.
A full copy of the LCD and other document can be found via this link.
WIA information on repeater licensing: link is here.
Note: This article is applicable to Australian (VK) stations only!