HUB is a unit that is used in order to expand the GROVE ports over the M5Stack device. For example, if we want sensors with different I2C addresses or output to 3 devices at the same time. (M5Stack device usually can output one device at a time to to limited amount of grove ports)
Notice: HUB is just a hardware expander, if you are looking for hardware and software (standard protocol) expander like I2C, Single-bus, please check PaHUB or PbHUB.
If you are connecting two I2C slave devices onto HUB that share the same address, you will have problem getting I2C data from both. The I2C addresses of the devices must be different, they can be changed manually by changing the resistor values.