Imo it’s mostly good for multiclassing. It gets a ranged touch attack that doesn’t need reloading and a few spells at level 5, so it can go well with a lot of other stuff and works well with the Vow of Poverty that the Ninja or Monk can take for instance, or other things that forbid you from using items, since they function as weapons(for the most part) but aren’t items.
I’m making a level 20 Gestalt, and on one side of the Gestalt I took five levels of Warlock and 15 of Paladin, and on the other side I took Ninja, and I went TWF spec, so now I have 7 attacks each round that each, if I’m flanking an evil creature, do the base 1d6+1, plus 10d6 sneak attack, and 7 Smite damage(14 against evil outsiders and such which is good since we’re in Hell) and even resolve against touch AC. For an average of 374.5 DPR.
I have no clue how to build the Warlock in any other situation, but it worked out well for me.