Three core cables are normally used for balanced loads (L1, L2 and L3). A four core cable would be used for loads where a neutral is required (L1, L2, L3 and N). Often the neutral will carry significantly less current than the line conductors (in a balanced system it should be zero) and a half sized neutral is used to save copper (three and a half cores).
Note: normally I would specify a three core cable for balanced loads (i.e. motors) and a four core cable for distribution; I’m not a big fan of the half core. In some instances (where there are a lot of harmonics for example), you would be looking at a neutral current which exceeds the line current and a double sized neutral.