Yea, the first posting was right. When you don't apply a thermal paste, your notebook temperatures will be higher than they are normally supposed to be. The thermal paste helps to keep the temperature down. As a result from no thermal paste, if you're exceeding thermal temperatures, then it can be quite bad; fires or melting the CPU or other components.
While your CPU may never exceed the thermal maximums if it's on low load, that's no reason not to apply the thermal paste. You ALWAYS want the temperature to be as low as you can properly get them.
There's no reason not to apply a thermal paste. If it were expensive, it might be a different story but it's really cheap and does more than what it's worth. Your friend simply doesn't know as much as he thinks he does, or he doesn't realize that it's still a good idea despite you're not exceeding thermal maximums or whatnot.