I live in an area where the soil shifts a lot, so overtime time patio has cracked and pieces have separated. Last year I noticed a toad hopping around at night, and this year, I found out four of them had moved in and made a home under the house with the crack as their front door!
There's a lot of clay in the soil and the area I live in experiences a lot of shifts in temperature and moisture throughout the year. As such, dirt gets washed away when it rains, and then it shrinks in clumps when it's dry. The house itself is on concrete piers, so it's not a huge issue; however, if the house isn't on piers then it can become an issue depending on whether or not you live on a hill, how much of the soil has eroded, etc.