If you want to do a good sales presentation, then you need to, of course, tell the potential buyers about the product or service. However, if you want to do a great sales presentation, then you need to tell them what is in it for them. In other words, you need to tell them how that product or service will benefit their lives.
In light of this, I would say a presentation should spend equal time talking about the product or service and the benefits of that product of service. For example, if you are going to sell a new computer, then tell the people about all the new bells and whistles. Tell them how fast it is and how powerful it is.
After you do this, tell them about how this computer will benefit and revolutionize their lives. You can tell them about how organized their lives could be, how much time they will spend, and how it will not even put a dent in their finances in view of the good price. It is important to keep in mind that all great sales end with the notion of "what is in it for me."