I’ve been involved with a number of wells that required that the casing be properly cemented. Sometimes it was because of state regulations but, mostly, it was because it was the right way to build a well. Cement makes a seal between the borehole and the casing, and isolates formations that you don’t want to produce or which are contaminated. There are a number of ways to place the cement, some right and some not so right. I’ve seen drillers set the casing on bottom and back a cement truck up to the top and dump. This pretty well assures two things. First, you will end up with cement at the surface, pleasing the county inspector. Second, the likelihood of cement getting to the casing shoe and making a good seal is pretty slim. It will bridge off somewhere, or just run down in stringers. Not good.
Another common way of placing cement is by using an outside tremie line. This works pretty well if you have a large enough hole. Some states require a much larger hole than necessary, so there’s plenty of room. You can set the casing on bottom, and not have any cement to drill out when you go back in.