The quest Replanting A Lily is a great example.It also grants less XP and a humanity loss. Attacking the latter just results in a fight with a stronger than average human that is entirely possible to win invoked bypassing the later fight with him entirely.
Attacking the former results in him assuming his war form and most likely killing you horribly. There are two doors that lead straight to the Hollywood sewer system, and can be used to go back and forth to the surface for blood refill/needed supplies.
