There may be several kind of "money". Not only devises that are all of
the same kind of fiat money.  From some account you can withdraw gold,
or shares.

You could have:
    (defclass value ())
    (defclass gold   (value)
        ((mass  :type integer :documentation "unit mg")))
    (defclass money (value)
        ((facial-value :type integer)
         (devise       :type devise)))

Then you would definitely want to do:

    (defmethod withdraw ((account account) (amount money))   ...)
    (defmethod withdraw ((account account) (amount gold))    ...)

(But actually, as it has been noted, since there are several kind of
withdrawals (atm, cashier, etc), you want to reify it).