2mm is fine and normally within measurement error. However, buildings should be designed to not fail disproportionately, so there isn't sudden failure such as

2mm is fine and normally within measurement error. However, buildings should be designed to not fail disproportionately, so there isn't sudden failure such as like with the Miami footbridge. Design errors can lead to sections being over reinforced or other issues which could lead to collapse with little warning, which is what the concern will be. Edit : also with cracks it depends on where they are and what causes with them. Cracks are normal for concrete and the size should be controlled through detailing. Where cracks are larger than this it can indicate whether there are issues in bending/shear. Structural design also often takes into account behavior of cracked concrete.