Long live grass !
Compared to tillage or chemical weeding, grass covering remains the best way of obtaining topsoil, meaning with strong biological activity (from micro-organisms to worms).
Its main advantage is it increases the soil bearing capacity (therefore the possibility of returning to the vineyards quicker after rain), to avoid erosion and leaching of soil and to slow down the sturdy vines, notably the young plants.
Nevertheless this must be controlled: too much grass covering can result in serious competition with the vines and to a decrease of the yield, notably under the rows (meaning under the vines where the water supply is at its best). This is why many wine-makers chose only to use it between the rows (inter-rows) or every other row. This also requires a great amount of tillage to limit the grass height and therefore prevent the creation of wet zones near the grape clusters which would eventually increase the risk of rot.
Once the cultivation mode is chosen, the only thing left to do is to decide whether there should be a natural or seeded grass cover. They both have their advantages. The “natural” one has the advantage of being …. natural … of course! It doesn’t require any specific work and all the plants that grow are naturally adapted to the region. Seeded grass cover allows for a specific need be provided to the plants, like with nitrogen for example, but this does require additional work to the vines.
Basically, grass is just pure happiness;-)