Silicon is basically a component of sand (silicon dioxide) and a very cheap material. The cost is in making it pure enough for electronics use, then drawing it into a monocrystalline ingot. So, wastage of material is not in itself significant, but the more wafers you can get out of an ingot the better you utilise the energy and time expended on making the ingot.
If the slicing process uses more energy and takes more time than to make the ingot, then it is a negative gain, though. In that case you would be better just to make more ingots and accept the wastage of sawing them up.
Thus, it differs from a situation where you are using an inherently costly material such as gold, where material wastage is the key issue. Here it isn't.