Ancient coins, made by hand, don't exhibit the near perfection of modern coins: they're neither perfectly round nor perfectly centered, they're often unevenly struck and frequently show signs of die movement between multiple strikes. None of these conditions add much to the interest, or the value, of such coins.
Brockages, though, where a coin has stuck in a die, unnoticed, and has impressed its image into the next coin struck, certainly can be very interesting, and can provide some clues to details of mint operations.
Notes
Roman Republic, denarius, Sear 176, RSC Claudia 2
Roman Republic, denarius, Sear 183, RSC Valeria 11