In order to make the internet practical, the field of web development is a must. It’s great to be able to connect one computer with another, however, before this connection is made useful, there has to be some sort of UI on the host’s end. This of course is where web developers come in and give the end user something to work with relevant to the type of site the user is attempting to access.
Web development is not something singular, however. Nor are web developers equally proficient or able to conduct the same tasks with the same set of skills. Modern web development has branched off such that, with respect to the preferences of a particular developer, a multitude of different design languages and tools can be used to create a web site for internet access.
That said, both of these categories (or rather, all three of them) play an important role in modern web development and internet use, and as such, are equally irreplaceable and mutually constructive. Whereas one particular type of application may require client side functionality, its counterpart may in fact require the opposite, and for this reason, both have permeated the web development industry.