One of the jobs in the vineyard this time of year is ensuring that the vines are well ventilated to benefit from the breeze to cool them down. Good ventilation protects against fungal diseases like powdery mildew which thrive in damp/moist environments.
It makes the vine roots dig deeper for water as we get rid of roots on the surface. This is important in dry parts of Spain where vines suffer "water stress" due to lack of water: it stops the fruits from ripening. Cutting the roots on the top layers of the soil gives an advantage to those roots digging deeper.