Thin cracks along a concrete foundation may be the result of settlement in the concrete and not necessarily be a cause for concern? What you need to pay attention to is the shape and direction of the divide. Long, horizontal splits in the concrete could indicate pressure from the outside — possibly from saturated soil — that would need to be repaired.
Normal settlement doesn’t generally cause horizontal cracks. Utilize a Structural Engineer for cracks that leak water or are wider than 1/4 of an inch (some experts put the limit at one-sixteenth of an inch). All cracks, even those that appear to be minor should be repaired. Your goal would be to stop all moisture from coming into the home through small cracks because water entering in will damage the steel inside the concrete causing it to rust and cause further deterioration.
Depending on the cracks in a home you could be talking about minor $ or major $ to fix. Always determine ahead of time what you are dealing with so it doesn’t surprise your pocketbook later!