It's buried somewhere in the huge PUP thread in General I think, but the text was pretty much copied verbatim to several wikis:
The automaton periodically checks the information around the automaton and decides its next move (if HP took a hit, it will cure, if TP has been saved up, it will perform a WS, etc.).
When using the Tactical Processor the frequency of these checks is increased and allows the automaton to respond to variations in its environment quicker and more precisely.
However, every time it performs a check, the overload value increases, so as the frequency of checks increases it will increase the possibility of an overload.