We always recommend pre slab inspection for your peace of mind. Why?
It is so that another pair of expert eyes goes over the preparation in case something was missed. Frequently we find inadequate attention to detail and even serious errors.
In the photo below, builder has failed to give the latest plans to the concreting contractor and the slab was poured undersize. What was the supervisor doing? What about quality control system? What system?
Whilst to builder’s credit, he made the error good and produced engineering certification, it is something that could have been picked up and avoided at a competent pre slab inspection.
I have seen a lot worse
If you are serious about protecting your investment then you should have independent stage inspections for your peace of mind.
Your call