Let’s start with the advantage of using opera
Opera is the internal information system of the property it contain all the data related to your property including guest history, reservations, in house rooms arrival rooms daily reports, monthly reports, billing, posting routing, also it can be connected to another systems such as Marsha Reservation System, Guest Ware.
About the disadvantage of using opera it can't be used outside the property as it is internal information system therefore the chain hotelier should have another reservation system connected to opera on each property, the independent hotels which have global reservations office but it is rare also should have another reservation system.
If you need any further assistant please don't hesitate to ask me.