You can completely cross off the topic of warranty. If your place sinks in 10-15 years, then that is entirely your problem, and no soil survey will help.
A geotechnical report never helps with something like this, as the ground conditions are always the builder's risk. It is still useful to obtain a foundation recommendation; otherwise, your general contractor will just do something like "30cm of gravel, we always do it that way.."
A soil survey report never helps with something like that, since soil conditions are always a risk for the builder. It is still useful to get a foundation recommendation; otherwise, your general contractor just does something like "30cm gravel, we always do it like that.."
My general contractor does a soil survey for every construction project, which I also consider very sensible.