Length of Copy
How much copy is enough? The easy answer is "enough to say what needs to be said". Better writers realize that the pace of a script is crucial to setting the tone. This contributes to, or detracts from, the quality of the image the client is trying to portray. It can also have an impact on the attention span of someone listening to a corporate or training piece.
Consider what you are asking your audience to do: Stop enjoying a program or doing their work to pay attention to your message. That is a tall order on its own. Do you really expect them to work hard at it? That's too much to ask. If it's a commercial, they will change stations or go make a sandwich. If it's an industrial, they'll mentally tune out or even switch it off.
Here are some rough guidelines on word count. For 60 seconds, 130 words = lots of inflection; 155 = typical; 180 = fast; 200 = maximum! Numerals, symbols, etc., count as one word each.
Think of your own reaction to reads that almost seem to blur. It's easy to tune them out. The closer you get to the top end on word count, the more people you can kiss goodbye.