What are the advantages of using the Flying Blue program?

Advantages are listed on their website, but in short:

• At low tiers, none at all except you can exchange your miles for tickets.
• At higher tiers, priority queues at check-in and boarding, and access to airport lounges, as well as all the benefits of the lower tiers (none).

And oh, you occasionally get an email with special members-only offers of discounted tickets on specific routes.

The most important advantage, which is never advertised: you have less chance of being kicked out of a flight, in case of overbooking (which is also now becoming rare). On the system to find who to kick out, the frequent flyer status (and miles/point) is taken into account.

But because there are many people not enrolled, it could save you some hours. [Note: having a connecting flying and having checked baggage are still more important reasons, so do not trust only being a frequent flyer, but it helps]. In theory, it works also on the other way: you could have more frequent upgrades, but because there will be probably some people who fly more often than you, the probability on getting them varies a lot on how frequently you flight.

Personally I'm enrolled on many frequent flyer programs (last being Flying Blue). No disadvantages, but to select the best flight, the frequent flyer program affects just the case of ties.

The platform on which you book a flight usually doesnot matter, but some very cheap flights are in a "booking class" that do no give you points.

There is one uncommon advantage (or used to be: I hear AF overhauled the system, so YMMV) with FB: the higher your tier, the more miles you accrue for the same flight, in the same class.

I traveled every 6 weeks HKG<>BOD for three years. When I started doing this, I was a so-called "Ivory" member, ie the lowest rank. I watched my account jump up and up and up, and became (again) Platinum within a year. This is when I realized that my flights were not credited with the same number of miles, even though they were always the same, booked by the same agency, under the same class. Every time I went up a tier, I got a bigger multiplier for my miles, separate from the multiplier you get when flying Business or First. Flying as a Gold member gave me, if memory serves, 125% of the actual mileage, and Platinum 150%. So I reached a point where flying HKG<>BOD in Business class as a Platinum member got me 22,000+ miles per return flight.

I haven't flown yet with another airline that does that. Also, the thresholds were lower for overseas residents (ie not living in France). I remember the number of qualifying miles for Platinum was 70,000 for overseas residents, and 90,000 for residents in France. That was quite uncommon too. Not sure whether this is still trues with the new system.