Small functions are easier to read, write, test, debug, and understand.
If it isn't clear from the name of a function or variable what its purpose is, document it with a documentation string and a comment. In fact, even if the purpose is evident from the name, it is still worth documenting your code. Lisp-oriented text editors include tools for ensuring balanced parentheses and for moving across pairs of balanced parentheses. The following functions often abused or misunderstood by novices. Think twice before using any of these functions.