A WiFi analyzer can help identify the channels that are already in use and how congested they are. By scanning for used channels, the technician can choose a channel with the least interference from other networks, which is fundamental for optimal wireless performance. Scanning for rogue access points or assessing the security mode does not directly help in choosing the best channel, though these are important considerations for overall network health and security. Measuring the distance between access points might be informative for the installation process, but it doesn't contribute directly to the selection of an optimal channel.