They do very well in enhancing the wallet of those that sell them. They make those folks that like to have the "best/newest of everything" feel very good about themselves.

I have 8 of them but none yet into an airplane. Digital servos idle at about the same current draw that analog uses for work. Having played with servos and current draw and watching what happens to a battery when several servos are loaded at the same time, I rather use my old analog servos. That was a main problem when NiMH first came on the scene. Even with analog servos, using several servos and loads at the same time, NiMH dropped too far below the needed voltage to force the current out there. Even for a brief period, such could cause bewilderment and "Wot tha' ELL?" in a pilot's mind, resulting in pilot disorientation and a crash.
In a very popular RC magazine that just recently left the playing field, a very excellent column writer discussed this topic at length. I guess that must of POed some of the suppliers and that superior column writer was very soon replaced with a much less informed writer. [:-]

Not about digital servos as they were not here at this time, but just servos in general: Some 20 years ago I was an agent for the World Engines Expert Radio, which, as a radio, was outstanding, but workmanship, materials etc. left a lot to be desired. I sold one to a coworker. I saw him a couple weeks later and he was complaining about the servos being slow. His club members, being unfamiliar with the radio, condemned it to death. We talked of other possible problems and I became aware that he had not sealed the aileron-wing areas, on his .60 size Dirty Birdy, IIRC. I told him how, and a couple weeks later we were working together again. He told me that after a couple flights those clubmembers were asking what kind of new servos did he buy and where could they get some. Troops, it is not always the equipment, but I suppose that is the best excuse.

Like in everything else it is basically what YOU want to do.