Isolators without sockets have the benefit of not needing RCD protection if the circuit is installed according to that purpose, saves fitting an RCBO if one was needed and money.

I remember years ago (they may still be fitting them) that they used to fit all-in CUs into low cost housing (shanty town housing). It was a CU with a couple of sockets, light switch etc. All they did was fit the CU and then run a cable to the light, job done, move on to the next one.