But why would i need it? Well some 3.3V sensors are not capable of handling 5V signals coming from some microcontrollers (like Arduino), these sensors can still be used, with a reduced life span. Additionally, you will also need to supply the I2C sensors with 3.3V , requiring an external power regulator making things more complex. All these problems are solved with this practical board.
In some I2C applications, the bus capacitance limit of 400 pF restricts the number of devices that can be attached and the wire length. Using the I2C Translator (PCA9306) enables the system designer to isolate two halves of a bus; thus, more I2C devices or longer wire length can be used.