The 1GigE era is coming to an end and is rapidly being replaced by 10GigE. This means that network traffic with different patterns and needs will merge together on the same network.
This may directly impact performance and predictability due to lack of isolation, scheduling and arbitration. Network I/O control can be used to prioritize different network traffic on the same pipe.
You cannot have a guarantee for a bandwidth as long as you don't limit other traffic so there'll be always enough available bandwidth.
As some traffic (that is, vMotion) might not be used all the time, we'll have temporarily unused bandwidth with the static limits. As long as there is no congestion this doesn't really ...