If your original voltage regulator is operating correctly your electrical system should be protected against harmful power peaks, your bulbs should last longer, the battery should be receiving a charging current while the engine is running and, last but not least, the battery should not discharge (too much) power while in standby. The voltage regulator units with more than 3 connections also function as AC/DC converters and can deliver a constant direct current supply.
If you are upgrading a VESPA model with a points ignition to an electronic ignition system the voltage regulator unit with just 3 connections is required. If your motor build project includes the COSA models stator plate then you will need to use the corresponding COSA models voltage regulator.