The garden has been designed to need as little maintenance as possible. The straw helps because it results in less wedding, less watering (not that we need help with that right now) and adding organic matter to the soil.
The straw means that any weed seeds in the soil get less light and so are less likely to germinate, and if they do they are much weaker. This means that there is much less work for us and it is much easier to maintain.
If soil is bare then when the sun beats down on the soil it will result in evaporation. The straw reduces the rate of evaporation from the soil, which means the soil stays much moister. Those few days when it was hot we could tell that the straw made a massive difference in how often we needed to water the garden.
The straw also helps to build up organic matter in the soil. This is really important to ensure good quality soil. If you have sandy soil and add organic matter in decomposes and helps with water retention. If you have clay soil it helps to break up the clay particles and it gets less sodden when it rains or drying out in the summer.
You can also use straw in your garden. Why not get a bale? If a bale is too big share it between neighbours.