My impression was that Skeleton Mages were generally not thought highly of, so in my summoner necro build I have no points assigned. But I am nearing the end of my ultimate build, only lacking Marrowwalk (I finally built an Enigma, found 2 SOJs), have maxed out all my core skills. With no obvious pressing need or place to put additional points, if I assigned a point to Skeleton Mages, I would be around level 15 from equipment, would there be any tangible benefit for doing that? That would give me 7 skeletons, 18 revives, 7 mages, a golem and a merc.
Generally the summon necro cast amp damage on everything for the skeletons and revives. Mages do between 400 and 700 elemental damage an attack with 20 hard points. So without lower resist on hell its not going to do enough to warrent the investment. However, the have a ranged attack and in large numbers they can widdle something down. Additionally they have as much health as you skeletons. So they make good permanent targets to draw fire with out the three minute experation dates of yhe revives. Last if you put bramble on your merc paired with amp damage they can deal considerable thorns damage. In short it comes down to if you have something better to spend your poinys on.