This question is so broad in scope that the answer is “it depends”. Subnetting really has no effect on LAN performance other than separating broadcast “regions”. Subnetting in a LAN is defined as a VLAN (virtual local area network). See <a href=”http://en.wikipedia.org/wiki/Vlan”>Wikipedia</a> for more information on VLANs. Subnetting may put more of a load on your LAN switch or router since it has to decide where to put packets now rather than letting devices on the same LAN talk to each other.
I think you should define what you are looking for with reference to “performance”.