A bonded membrane to the outer shell has three main benefits. The first is that it offers better breathability. Next, it has less water pick up so the garment stays lightweight and dries more quickly under wet weather conditions. And third is that it prevents cold (from the soaked outer shell) from being transported to the body.
This is a true blessing, especially for long distance commuters and adventure-touring riders that predominantly ride in cold and wet weather conditions. Less water pick-up automatically implies that the item dries quickly and is ready for the commute back home at the end of the day or to continue your trip in comfort.