A student's question

My teacher keeps drilling into our collective heads that using the break command is harmful, and that if we wish to terminate a loop early it would be far better to create a boolean variable, set it to 0, and add a condition to the head of the loop, and set the boolean variable to 1 when a break is needed. Note that this way you actually have to check this every single loop (where it is not needed almost every time) as well as waste a command to reset the boolean in case it was set to true.

Is there a reason to this?

>>92
>>92

(defun f () 2)
(f) ; 2
(defmacro m () '(f))
(m) ; 2
(flet ((f () 3)) (m)) ; 3

(define (f) 2)
(f) ; 2
(define-syntax m (lambda (stx) (quote-syntax (f))))
(m) ; 2
(let ((f (lambda () 3))) (m)) ; 2