Are you buying a computer or planning on building one?
If you are buying one then your operating system(windows) will likely already be installed so you would not "NEED" one. Especially seeing as how most programs can be bought online and downloaded with a decent internet connection.
If you are building one and plan on using windows then you will have to hook one up to install windows since windows can only be found on dvd(I may be wrong). You could however unplug and remove the optical drive after everything is installed.
However, optical drives are so cheap these days that there is little reason to not have one. Especially seeing as how almost any computer program you buy at a physical store will come on a cd/dvd. If you just don't want one because of the aesthetic value you could always get a portable dvd drive that you could hook up only when it was needed.