[lispm]

Macros only really slow down things when you for some unknown reason call EVAL on source code many times.

When code is running using EVAL and an interpreter, macros can be expanded once and then the expanded code is used next time. For example in a loop it is not necessary to expand a macro each time it is used.

If one needs to EVAL new code all the time, then one may ask oneself if that is really necessary. For example if one is doing some kind of genetic programming. Otherwise it is basically a programmer error to do so.

I haven't seen any convincing example where it is really needed. My Symbolics Lisp Machine (which comes out of the MacLisp tradition, which had FEXPRs) got only limited FEXPRs (can't be compiled, can only be used at the top-level). Still the developers who had extensive FEXPR experience with Maclisp, were able to write the compiler, the garbage collector, the graphics driver, the window system, the network system, compilers and interpreters for various languages, text editors, mail clients, mail servers, and much more without using FEXPRs.