What is the purpose of a Pergola?

What is the purpose of a pergola?

Pergolas may come in a variety of styles and sizes, but they share the same primary purpose: to protect homeowners from the harsh elements. This could come in the form of shelter amid a spring rain shower or a layer of protection to block out the sun's harsh rays in the summertime. 

The purpose of a pergola is just to provide an area for you and your family / friends to mingle in.  You can choose whether you want to use it as an area to entertain, or if you want it to be a more private area to relax in, which can act as a respite from the world. that's why pergola is so popular in market.