[mng2]

I wouldn't call it 'scary', myself, but it doesn't strike me as a particularly useful feature. In software, a single slow subroutine can simply take up more cycles. But in hardware, a slow path becomes your critical path, and you have a hard clock cycle requirement. (Sure, you can use multi-cycle paths and/or change clock speed, but those generally have to be adjusted manually/physically, and not all design situations will have that flexibility.)