Thereby doubling your difficulties in generating names.
(Relative to epic fantasy, of course, where you can get away with first names and maybe a byname.) All right, bit characters can be Miss Smith and Mr. Brown, but main characters will have a last and a first. Which are not only all the adventures of picking the right name, but making sure they harmonize without being so blatant about it that the reader will notice.
Then you can get into adventures in determining proper usage. When and where will characters use the first or the last. Chesterton, who was a Victorian, denied that using a woman's first name necessarily meant you were a wooer -- just that you were a particular friend. He commented on how much more it meant that the way the Bright Young Things would casually call each other by nicknames on the slightest of acquaintances. Subtleties are useful but you have to keep them going all the time. (One flaw in the first Pirates of the Caribbean trilogy was that they would use titles and addresses when it added something -- Miss Swann vs. Elizabeth -- and then drop it when it did, so she was Elizabeth to everyone.)
It can have its effects. I've had crits where the critter commented that it took him a bit to figure out that the reason the names changed was the POV had changed to someone who thought of a character differently, but they were always impressed by the effect once they worked it out.