One reason I've heard is, that it;s still possible to get caries below the the sealing but the dentist (or you yourself) won't be able to see it by a purely vis

One reason I've heard is, that it;s still possible to get caries below the the sealing but the dentist (or you yourself) won't be able to see it by a purely visual inspection. At least here (Germany) you won't get an x-ray at every checkup.