If your home’s foundation is a ‘slab on grade’ foundation, that means that the foundation is resting on the ground. If that soil is considered expansive, the soil will change in volume with the moisture content of the soil. The soil will contract or shrink as the moisture content of that soil gets drier. As the soil re-hydrates, the soil will expand or swell. The foundation will move up or down as the moisture content of the soil changes.
Because most of the evaporation happens along the edges of the foundation and it will take the water longer to flow from the middle towards the edge, most of the movement happens first along the edge of the foundation. (Now this discussion is only pertaining to slab movement due to normal weather conditions and not to other causes like a plumbing leak under your slab.) The reverse is also true when we have a pattern of rain happening more than normal, water will take longer to flow from the perimeter towards the center.
Since the edge of the foundation will move up as the swelling soil gets wetter and the edge will move down as the soil becomes drier, keeping the moisture content of the soil around the perimeter of the foundation constant will help keep you home from getting those hairline cracks in the sheetrock, brick and tile. It also will help keep the doors and windows from rubbing against the jamb.
How do you check the ground around your slab to see if it is too wet or too dry? There are many gauges and meters that you can buy from hardware stores, nursery stores, etc. Some of them are cheap, others will cost quite a bit. There is a way that may not cost you anything. I use an old screwdriver that I had broken the tip of. I walk around the edge of the house and push the screwdriver into the ground about every 10 feet. If the screwdriver comes out of the ground dripping water and mud, maybe I have been watering too much. If the ground is so dry that it is difficult to push the screwdriver into the ground an inch or two, I need to water more. If I pull the screwdriver out of the ground and it is a little muddy, perfect!
