So depending on the altitude selected to fly you either "have to" maintain in sight of the surface or not.
E.g if flying at 2500 feet outside CAS, I must remain in sight of the surface if I cannot be sure that I will be 1000ft vertically from cloud or 1500m horizontally?
At 3000ft+ I have to follow the more "tighter" regulation of 5km viz, and 1000, 1500 respectively? BUT do not need to be in sight of the surface?
You can look at it in many ways as to how "tight" things are. Below 3,000' you can follow the same regs as above 3,000, but if in sight of the surface you are allowed lower minima provided you are in sight of the surface - made a lot of sense today, at 2,500' it was gin clear, below more than 5K viz, but not a lot more and patchy cloud about 2,000', this meant a basic PPL could fly in clear air at say 3,500' and let down legally and safely on arrival.