LAT (Local Address Table)

LAT is a set of IP address ranges that describes all IP addresses of your LAN. Using LAT, it is possible to create rules that will not count traffic between hosts in your LAN. Having created LAT, you can refer in the rules to the addresses listed in LAT as "IP addresses of my LAN" and to the addresses not listed in LAT as "IP addresses of WAN".
 
If LAT is blank, the rules included "IP addresses of my LAN" will never work and the rules included "IP addresses of WAN" will be considered as "Any IP address".

You can get to the LAT from the menu Traffic -> Edit filters...
 
 Ctrl+N

Scenario:
You are a network administrator of the small network connected to Internet that includes NAT router as an Internet Gateway (192.168.1.1), local Intranet Webserver (192.168.1.2) and four client PCs (192.168.1.3-192.168.1.6). You need to do IP traffic accounting on who how much is using your Internet Connection. You don't want to count the IP traffic between hosts in your LAN.

Solution:
You should create:
- The LAT with scope 192.168.1.1-192.168.1.255
- Four filters with rules "192.168.3.x-WAN" (one filter per host in your LAN)

Filter No. 1.
Name: Internet traffic of Host 1.

Filter No. 2.
Name: Internet traffic of Host 2.

Filter No. 3.
Name: Internet traffic of Host 3.

Filter No. 4.
Name: Internet traffic of Host 4.