Initially this was the reason and I still do this, but it should be noted that Racket, for example, will treat the following examples exactly the same and will

Initially this was the reason and I still do this, but it should be noted that Racket, for example, will treat the following examples exactly the same and will do just fine with the non-tail recursive example (as far as I can tell): (define (sum/recursive/opt lst [sum 0]) (if (null? lst) sum (sum/recursive/opt (rest lst) (+ sum (first lst))))) (define (sum/recursive/non-opt lst) (if (null? lst) 0 (+ (first lst) (sum/recursive/non-opt (rest lst))))) I don't use any other variants of Scheme with any meaningful frequency, but I still use the uppermost variant because I'm just used to it.