DMs use voices many times to make a character unique. From the gravely voice of the barkeep, to the british accent of the scholar, they make NPCs seem to come to life just a bit more for the players. The question is, should players themselves use them?
First, let me kick things off by saying that my take on this is yes and no. It really depends on the character, and the player as well. PCs are “unique” by their very nature. Unique is in quotes only because to many players don’t actually make unique characters, but to those around them, they’re unique. If Bob plays a fighter, then you can see Bob and know who that is. The unique voice is unnecessary to make Bob unique. Sure, if Bob is playing a foppish swashbuckler, then Bob might want to do his best Errol Flynn impression just to add to the tone of the character, but does he really need to? I don’t think so.
However, character voices come in very handy in other game situations. For example, let’s say you base a character on Doc Holiday. Let’s make it a western campaign, and the DM approves you playing real western figures, so you’re playing Doc Holiday. So, after doing some research on Wikipedia (hey, it’s fast and cheap), you find that Val Kilmer’s portrayal in Tomestone is pretty accurate, so you watch the movie and learn to talk with that thick South Georgia accent (and, for the record, not all of us from down here talk like that. Doc Holiday’s home town isn’t that far from my home town of Albany, GA). Now, you talk about being someone’s “huckleberry” and that they’re a “daisy”. In this instance, that odd voice goes lightyears to bringing Doc Holiday back to life.
Now, it’s important that a voice not be a crutch to get out of proper role play. With the Doc Holiday example, he still needs to drink and gamble as primary ways to spend his time. The character can not be the voice, and the voice can not be the character. There has to be more substance. However, with proper substance and the voice, the character can come to life in ways you never even dreamed of!