Clojurist, technomancer and Leiningen creator, Phil Hagelberg does a nice job of dissecting "two ways to compose a number of small programs into a coherent system". Read the original in which three programming methods are compared. These are my notes, quoted mostly verbatim:
The Unix way
Consists of many small programs which communicate by sending text over pipes or using the occasional signal. Around this compelling simplicity and universality has grown a rich ecosystem of text-based processes with a long history of well-understood conventions. Anyone can tie into it with programs written in any language. But it's not well-suited for everything: sometimes the requirement of keeping each part of the system in its own process is too high a price to pay, and sometimes circumstances require a richer communication channel than just a stream of text.
The Emacs way
A small core written in a low-level language implements a higher-level language in which most of the rest of the program is implemented. Not only does the higher-level language ease the development of the trickier parts of the program, but it also makes it much easier to implement a good extension system since extensions are placed on even ground with the original program itself.