This applies to driving finish nails, those without heads and designed to be countersunk and filled with putty before painting or varnishing. Driving common or box nails, those with big heads, is easier because the heads are, indeed, big, and there is less need for care because it is, after all, rough carpentry. Some hammers, such as a framing hammer, have a checkered face, which keeps the hammer from slipping off the nail. OK, but try finish work with such a hammer, and if you drive the nail too deeply, you will end up with a checkered dimple, not something you want on finished woodwork. Another hammer might have a rounded head, designed to allow a final driving of a nail without such dimples.
Trouble is, try driving a finish nail with a rounded hammer head.
So, be safe and buy or use a flat-head hammer, and for goodness sake, stop driving before the nail goes flush with the wood. You can stop there, and use a nail set to countersink the nail. One more thing. Some old-time finish carpenters, instead of filling nail holes with putty, cut out a sliver of the wood, leaving one end intact to act as a hinge. They pull up this sliver, drive and countersink the nail, and glue the sliver back in place.