Well it would let every type of character have something to morph into that would further their attributes but would sacrifice public life.
Werewolf = Strength
Vampire = Stealth
Lich = Magic
No offense, but that is incredibly short-sighted.
Werewolves are very strong, very fast, and very stealthy. The only problem is that you can't loot, you have to kill a man/mer/beastman, and you can't use magic. A werebear would be a bit of an opposite. While they would still be faster than a normal human, I'd say they're more about having incredible strength, superb endurance, and high defense than being a very stealthy killer with high damage. Yet, a lycan can still integrate into society during the day, just as long as they get away from civilization during the full moon.
Vampires run the gambit of being extremely strong, magical, or stealthy, along with variances between those three (depending on the clan-strain). There are vampires more adept at healing, magic, killing, sneaking, all-rounded, or hiding in plain sight. Though vampires, in general, will be stronger, faster, and more stealthy than non-vampires. However, they are rejected by most of civilization (save for magical guilds), and they take sun damage (save for a recently fed Cyrodiilic vampire).
As for liches, the process isn't done for magical gain or power, it's done for immortality (dying a natural death is annoying). Lichification is a means to continue to pursue an end, and it is irreversible. They are universally hated, except may a select few (but don't count on it).