Originally Posted by smata67
The Ranco has a 2 degree offset to prevent over-cycling.
The offset/differential setting is no help against 'short/hot cycling'. This is where it starts up again very shorty (<5 minutes) after it has just finished running. This can kill a compressor in a matter of hours, or less. Short cycling can easily happen as a result of events like door openings, temporary power losses, or the probe coming loose.
A controller with ASD has a built in delay (usually adjustable) to prevent 'short cycling'. With ASD, it is possible to set the temperature differential/swing as low as 0.5F without worrying about short cycling. The mass of the beer keep cycling frequency well within limits.
The Johnson digital controllers have ASD, as do the $15-25 ebay DIY controllers. The $25 one is even dual stage, and will automatically switch between heating or cooling.