On gentle slopes, a tight fence, hedgerow, or vine-covered fence will block some of the air flow. Thus, the advantage of air drainage is lost. Strong winds are a handicap to some tender plants. Such plants are injured by cold winds and frequently they are blown over. Around the house and garden there are many little swirls of wind and some quiet places.
Tight hedges reduce wind velocity considerably.
If the wind strikes a wall, it may swirl vigorously around the corner of a house. You can identify these spots of low and high wind by observing where snow or dry leaves are blown away and where they accumulate. In my own garden there are some spots where I cannot put the kinds of plants that are hurt by winds. Practically every garden is unique in this respect. One of the functions of both low and high evergreens is to help buffer the wind for other plants.