vilas
You get me wrong. I don't think at all it's useless to activate when flying selected. I only said that it's useless to check the activation on PFD if the speed is selected, because you cannot check it in that case.
I personally use selected speed in most of the time. Computer is a computer and it still cannot think like a human being. For computer every airport is the same, it just follows database. If you often fly to some airports which use vectoring, computer just cannot cope with that because it cannot predict vectors. And man can expect what the vectors will be and arrange his approach accordingly.
If I am not speed restricted, I can play with the speed and make whole or most of descent and whole approach on idle thrust. During approach if you need little bit higher rate, you can add some speed and if you need to reduce the rate, you just decrease the speed. With managed speed, you will be most of the time in speed mode and accordigly the fuel burn will be higher than on idle. If you save 50 or 100kg per approach, multiply it by every flight you make throughout the year and you will save big money for your company. The bad thing is that only few companies award you for this
Computer is just not good enough yet to fly descent and approach on idle thrust