Simple code to demonstrate this:

;; -*- lexical-binding: t -*-

(defmacro my-macro (x)
  `,x)

(eval-and-compile
  (defun my-func-eac (what)
    (my-macro what)))

(defun my-func-normal (what)
  (my-macro what))

(print (symbol-function 'my-func-eac))
(print (symbol-function 'my-func-normal))

`eval-and-compile' is advertised in Elisp manual to make byte-compilation
of certain macros without prior loading possible. Looks strange that at the
same time it can worsen performance of non-byte-compiled code.

Paul