It depends on the airline. A few years ago, when I used to fly and average of at least one round trip per week, including many from the US to Europe it would get me: - Free domestic upgrades to business class - Access to showers in the airport, behind security - Hot food and free drinks in the lounge - Priority access for boarding and no baggage charges - Early access to seats for reward usage (including transatlantic business class upgrade) - Access to excellent ground agents to help adjust itineraries, including frequent waiver of change fees - A nice quiet place behind security to wait during layovers

That was basically SA gold. If you are higher tier (e.g. LH HON Circle), then add things like free full service restaurant and private passport control to the list.