When you have 3 or more Exchange Servers in an Exchange Site, the naming of your Exchange Servers will affect the amount of network traffic generated by the KCC (Knowledge Consistency Checker).
Each Exchange Server runs the KCC every 3 hours, to contact another Exchange Server to verify its' knowledge of other Exchange Server computers in the site.
If a site has six Exchange Servers, which server the KCC contacts is based on name, so that JSI1 contacts JSI2, JSI2 contacts JSI3, JSI3 contacts JSI4, JSI4 contacts JSI5, JSI5 contacts JSI6, and JSI6 will contact JSI1. If JSI1, JSI3, and JSI5 are on one subnet, while JSI2, JSI4, and JSI6 are on a different subnet, one full KCC cycle will cross subnets 6 times.
If however, JSI1, JSI2 and JSI3 where on the same subnet and JSI4, JSI5, and JSI6 where on another subnet, a full KCC cycle will only cross subnets 2 times:
1. JSI3 across to JSI4.
2. JSI6 across to JSI1.
The more Exchange Servers that you have, the greater the gains realized by naming to minimize subnet switching.