Stewart has a recent post up about whether writers can also act, in the context of reading their own dialogue and such. This reminded me of something from my writing youth [cough] and since it's not really relevant to his post, I'm putting it here.
Twenty-some years ago I was in a (realspace) writing workshop and this one woman participant was a very expressive reader. I found her too slow and annoying to listen to for that reason, but she "did" voices very expressively. A lot of the workshop's writers thought she was just wonderful and wanted her to read their stories for the group (the workshop format was to have stories or chapters read right then and there, and then commented on) because her reading made the stories sound better.
I tried to argue that this was a reason not to have her read their stories. The whole point of being in the workshop was to focus on the writing, its good and bad points, and how it could be made better. If the person reading the story is so actor-y that the focus is on the voices and the characters as expressed by the voices, rather than on the writing itself, then that makes it harder to concentrate on the words as they appeared on the page, and give proper criticism.
Of course, I was ignored and a number of people had this woman reading their work for the next few months. Whatever.
But there are going to be times when a vibrant show of lively talent really isn't what you're looking for. If a story has been published and you're doing a reading for prospective buyers to try to persuade them that said story is wonderful and delightful and worthy of their money and time, then getting a really excellent reader to do the performance is probably to your benefit. In a workshop environment, though, where the purpose is to focus on the words and only the words, allowing distractions (no matter how entertaining) is counterproductive. The bare words are what you want in that sort of situation, and if they come across as boring then you need to know that ASAP, not have it masked by a character-actor of a reader.