The smart charge function on chargers checks the charging conditions of the batteries, the temperatures of both the batteries and the charger, etc. This allows the charger to individually charge each battery under the best conditions.
This function shortens the charging time by 5% compared to the chargers without such function. Keep in mind that the charging time varies depending on environmental factors and ambient temperature*. It could be the case that the smart charge function does not work depending on the condition of the batteries (e.g. When a battery has degraded).
* This was tested by Panasonic using the BQ-CC08 (launched in Japan in November 2011)