In Windows XP and Windows Server 2003, it was common to modify the following setting or the registry key:

To maximize data throughput on the server for network applications
1.In Control Panel, double-click Network Connections, right-click Local Area Connection, and then click Properties.
2.Select File and Printer Sharing for Microsoft Networks, and then click Properties.
3.Under Optimization, select Maximize data throughput for network applications.

The corresponding registry key is:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management
LargeSystemCache (dword) 1(hex)
Note:  Default setting

In Windows Vista, Windows Server 2008, Windows 7, Windows Server 2008 R2, the gui has been removed.
And the registry is there for backwards compatibility for apps that check it.
But the code has been deprecated.

So do I need to modify this key on Vista and higher?
No.

More information:

Maximizing Data Throughput for Network Applications
http://technet.microsoft.com/en-us/library/cc728171(WS.10).aspx

LargeSystemCache
http://technet.microsoft.com/en-us/library/cc784562(WS.10).aspx