When a partition doesn't need all of its allocated bandwidth, PacketWise always lends excess bandwidth to other applications in need.
For example, let's say you have two partitions:
Partition A: 256K partition, allowed to burst up to 512K. Partition B: 256K partition, allowed to burst up to 512K.
If a user in Partition B is using all of its 256K and needs more bandwidth, and a user within Partition A is using only 56K of its guaranteed 256K, the user in Partition B is allowed to access the unused bandwidth in Partition A.