[bunderbunder]

There's really just one justification, but it really is an interesting one: It gets the logical structure of the code in line with its lexical structure.

One reason this is neat is that it facilitates language extensibility to a radical degree. LISP has its macros, FORTH has its compiling words. Languages that allow infix syntax have tried to come up with something similar, but I haven't personally used one that I thought was particularly successful.