They allow you to connect two hose pieces or gather your filtration equipment to the supply pipe for drinking water.
The quick release is very convenient to connect the hose to the fitting without fear of leakage. It supports high pressures up to 10 bar.
1/4 inch connections are mainly used in reverse osmosis systems of communication, because their small diameter decreases the flow rate of the water to improve the filtration efficiency.
For 5/16, it is exactly identical to the diameter of 8 mm, thereby making the switchable fittings.