The entertaining speech, to me, is a speech purpose which needs added attention.
Yes, it is outlined as one of the four general speech purposes. However, I don't believe it should have it's own category, and yet, it should - but be more than only that.
Here's what I mean:
On the first count, I don't support the notion that it should have its own category because I believe every professional communication should be entertaining, no matter what the topic. It's your fundamental responsibly as a good speaker to build any presentation that way.
Let's use an informative speech as an example:
You can give a dry account of the safety procedures that must be taken in order to put up a cell phone tower;
You could give that same presentation, interlacing it with descriptive word pictures of the vistas you experienced from that altitude. Perhaps you could see the ocean, or a certain group of islands, or a hang glider launching nearby. Be as illustrative as possible. The information can be given in its entirety, as well as bringing life to the presentation.
The second count of contention I have regarding the entertaining speech is that it must do more than just entertain.
To prattle on about a topic that only entertains is very weak. It carries no weight, no substance. A speaker who does nothing but give the audience a bunch of fluff is not going to be held in high regard for very long.
So, the "entertaining" communication has to incorporate something deeper, more wholesome, that the audience can take home and reflect on.
A story about a 12 year old child's birthday party;
A story about a 12 year old child's birthday party, 3 weeks before she was scheduled for chemotherapy.
Both will be entertaining, yes. However, only one will have meaning.
Now these are only examples to illustrate my point. Your rendition need not be so dramatic, of course it must be real and authentic.
Realize the importance of giving a presentation which allows the audience to apply meaning to it verses a story that lacks depth. Also, the effect of an informational demonstration that comes to life compared to one that remains dry.