To do a voice or not?
Should I have an accent? Talk in a particular way? Use particular words?
Voices can make a player feel very connected with the paper in front of them. Having them speak in a haughty tone could really drive home the arrogance. Consistent mispronouncing a word repeatedly could drive home age or mentality of a character just as much as it could show intelligence or lack of care.
They can, however, be a two edged sword.
Be careful with these. A person who has faced difficulties with speech in the past may not feel comfortable with someone mimicking that particular facet.
Using a regional accent could mean accidentally offending someone who identifies with that accent.
Using a voice of another gender should not embody gender roles. A Man shouldn't talk about how he is strong "I'm a man I'll protect you!" nor should a female talk about things in form of her weaknesses "Oh no! Somebody save me!" There may be exceptions to these, but carefully decide if you are saying what he or she would say, or if you are saying what you think society says they will say.
Any time you choose a voice to utilize, recognize that you could very easily become a caricature. If your customization marginalizes, generalizes, or demeans the population is belongs to, then you are probably doing it wrong.
Any time we roleplay, we grab a piece of another human being and try it out, like a shirt. However, just like skin color, there are parts of us that we can't change.
Here are some tips:
If you sound like Yoda and use grammar and other sounds to distinguish your voice, most will recognize it, and it is hard to offend. If you are basing it on a character that is a caricature (Like a Looney-Tune or Simpsons character) then you risk offending someone, even unintentionally. The reasoning here, is that these satirical characterizations of people spin their humanity in particularly deviating ways, making them clearly good or bad.
Voices add a lot of depth and memorable moments to campaigns. Include them! Just remember that the primary focus should be on collective story telling; someone who is hurt or distracted by your voice cannot fully focus on the fun.