The overlap between open source and closed source

Question

I would like to understand why do some people like open source and some others like closed source? Let me be more specific and make my question about web development. If I build my site using an open source server side language what are the benefits for me? and if I build it using a closed source server side language, what are benefits?

I just want to understand how can I choose between the two differnt paradigms when building different types of web sites and applications!