I would wager he is refering to the 1.6 ECU relocation - which is a very, very commonly performed alteration.
The ECU from factory sits on top of the forward cam above cylinder 4 and the ECU is well known to suffer from heat-soak associated with it's location right on top of the engine.
The heat causes solder joints to crack / break or even the solder to soften to the extent that the pins begin to fall back down through the circuit board, losing their connection to the plug on top. It causes all sorts of havoc when it happens too.
People typically relocate the ECU towards the battery box or bulkhead as a cooler, safer location for the 1.6 ECU.
It's not necessary to do this on other models.