A good deal for the airlines, yes. I see no postive benefit to the pilots of any of the three airlines. There will be little or no growth in jobs, in fact, the airlines will probably shrink even more as they cut out flights on routes where the three overlap.
The main reason CO, DL and NW have got together in this alliance is to be able to compete with the two other major international partnerships, Star Alliance and Oneworld.
It is more a marketing exercise for survival than a cost cutting one. Continental and Northwest share many routes but still compete on them.
There is a strong likelihood that KLM, Air France, and Alitalia will all become part of this group.