Great question, What a Digatron gauge does is allowing you to monitor the quality of your combustion from a temperature standpoint. As your Air to fuel mixture leans out the combustion temperature raises. And likewise as your Mixture richens the temperature lowers.
You have probably heard of guys melting down their engines for various reasons.... These types of gauges allow you to determine proper air/fuel ratios so you don't run the engine too lean, thus causing a piston failure. Aluminum melts around 1340 degrees, so keeping it well below that is critical. Depending on your use, somewhere between 1150 and 1250 is ideal.
The Digatron gauges are designed to record the parameters of your engine and allow you to review them on the gauge and/or download the data to a PC for analysis.
Their are built in warning lights and limits that you can program into the gauge to give you a visual warning if a problem presents itself.
Things like Altitude, Fuel quality, ignition and clogged carburetors or injectors among others can cause a lean condition.
The Digatron gauge gives you the information you need to head off a potential problem. Not to say it is a cure against meltdown... It is a tool which gives you the information you need to make your informed fueling decisions.
Hope this helps.
It is a brief outline of why to use an EGT gauge.
I am sure other SF guys have more to add.
