Not really, some sand can be bad but if it is plant safe it is a good practice. The roots generally need the moisture as i understand it, top layer of soil drys real quick so roots don't bother so much, the layer of sand keeps that top layer moist for longer so roots use it, they love the top layer cause it is a good source of air too, not waterlogged like the bottom is a lot of the times. This is my simplistic point of veiw but at the end of the day pebbles, hydroton, sand, wood bark (used in parks and flower beds everywhere) or any kind of mulch will do and saves time cultivating.
Hydroton pebbles were my favourite but i like to see and feel the surface of my soil, i cultivate very well so i get a bit of root growth near the surface with no mulch, roots love the light airy cultivated soil. I found a danger of using a soil mulch or cover was that sometimes it promoted mold and damp conditions. Humidity and temperature are also points to consider, i don't really need it here in wales, its always humid, wet and never too hot, desert regions would have to have a soil mulch to keep the soil moister. Read up about it.
A little trick i do with my soil if it is stubborn and can get a little muddy and lumpy straight after watering is to cultivate two days later as well, this futher cultivates the soil and gives it time to dry just a little and become a little more manageable. I use flowering compost from a good supplier, my cultivated top layer is always springy, loose and even textured for about an inch but i am religious about my cultivating.
