One difference is flow control. When you call a function, all the arguments are evaluated before being passed into the function. If you want to delay evaluation, you have to wrap the argument values in a function. When you call a macro, the text forms get passed with no evaluation. Say Clojure forgot to ship with the boolean "or". "or" should evaluate its arguments one at a time (to allow for short circuiting) and return the first non-false value. You could do this with functions, but you have the source-level overhead of manually wrapping everything, and performance overhead of defining and passing an anonymous function for each argument. With a macro, at compile time you just translate the "or" macro into a simpler form that uses "if". This is how Clojure actually implements "or":

    (defmacro or
      "Evaluates exprs one at a time, from left to right. If a form
      returns a logical true value, or returns that value and doesn't
      evaluate any of the other expressions, otherwise it returns the
      value of the last expression. (or) returns nil."
      {:added "1.0"}
      ([] nil)
      ([x] x)
      ([x & next]
          `(let [or# ~x]
             (if or# or# (or ~@next)))))

Also check this http://lists.warhead.org.uk/pipermail/iwe/2005-July/000130.h...