Harmony is the only character that started in the first episode of Buffy and ended in the last episode of Angel. The AI team that took over Wolfram & Hart appeared to be all geniuses - Gunn became a walking legal compendium, Wesley and Fred were established researchers, Angel became CEO, Spike was his old competitive self, Lorne managed entertainment but Harmony was a secretary for Angel and seemed to be her established self - a follower, not a leader - and she became one of the people who would represent the non-professional, ordinary type of people. She was a lot of fun whenever she showed up either being one of Cordelia's gang in high school, Spike's disposable girlfriend later, the finder of the Ring of Amarra, the classic bitch-slapping, hair-pulling fight with Xander or a Wolfram & Hart employee.
I put Harmony in the same class as Spike - not people I would like, but when these characters show up in the story, you know it is going to be fun.