It's fine for outlining -- usually -- where I call the characters "-" or "--" or "---". But when I am actually writing, I need a name. Frantic hunts through lists of names and baby name books are not unknown.
It might be kind of ironic for a bit character, or even a piece of the back story who will never appear onstage -- but then, names are vitally important for those characters because they have so little else to counterbalance them. They're that important for major characters only on introduction. (I once read an article on naming soap-opera characters that commented that if you're introducing the mayor, you can't name him Lefty, but if you have a character named Lefty, he can run for mayor, and win. First impressions are so important.)