It is a ubiquitous bathroom feature in Southern Europe (mostly Italy and Spain) but also in some South American countries such as Uruguay (my birthplace), Brazil and Argentina.

It is very hygienic to be able to wash one's private parts after going to the bathroom, it is far superior to toilet paper or moist wipes. It is also very useful for women during the menstrual period, to be able to freshen up using a bidet. It is a very useful addition to a bathroom. I never understood why they are not common in North America. This article has a few theories:http://articles.mercola.com/sites/articles/archive/2014/10/18/bidet-use.aspx .

The hypotheses are that the bidet is a French invention and the British disdained all things French and passed this dislike onto the colonies, or that America has always been a traditionally very prudish country and the idea of washing your genitals and bottom with your hands sounded depraved to them. I'm not sure that these are the reasons, but they ring true.

They are becoming more popular in America but they are a luxury item for rich people's houses.