Gulliver encounters the Houyhnhms in his final voyage in a world where there are the Houyhnhms and the Yahoos. It is clear that the former group are greatly civilised compared to the Yahoos, who are shown to be savage and vicious. The Houyhnhms have established a world that greatly appeals to Gulliver as they live a life where reason is ther guiding compass rather than emotion. The advantages of such an approach are shown to be very attractive, as these people do not lie, deceive each other and they are not subject to other vices. However, perhaps the satire in this journey lies in the fact that, although they are shown to have significant advantages, they also have distinct negatives, as their reason-ruled lives have no place for love or fairness, and there is no real concept of family love as a result.
The world of the Houyhnhms therefore is shown to have distinct advantages, but really I believe Swift is showing us the consequences of living a life that is totally based on reason and where emotions have been erased. In spite of the benefits of such an approach, Swift is really saying that we would not be human in the same way, as part of what shapes us as humans is our emotions and our capacity to love and empathise. Lacking these abilities turns us more into unfeeling robots rather than civilised beings.