Pedant and quibbler that I am, it annoys me when I hear professional philosophers use the phrase 'Leibniz's Law.' My reason is that it is used by said philosophers in three mutually incompatible ways. That makes it a junk phrase, a wastebasket expression, one to be avoided. Some use it as Dale Tuggy does, here, to refer to the Indiscernibility of Identicals, a principle than which no more luminous can be conceived. (Roughly, if a = b, then whatever is true of a is true of b, and vice versa.) Fred Sommers, referencing Benson Mates, also uses it in this way. (See The Logic of Natural Language, p. 127)
Others, such as the distinguished Australian philosopher Peter Forrest, use it to refer to the Identity of Indiscernibles, a principle rather less luminous to the intellect and, in my humble opinion, false. (Roughly, if whatever is true of a is true of b and vice versa, then a = b.) And there are those who use it as to refer to the conjunction of the Indiscernibility of Identicals and the Identity of Indiscernibles.
So 'Leibniz's Law' has no standardly accepted usage and is insofar forth useless. And unnecessary. You mean 'Indiscernibility of Identicals'? Then say that. If you mean its converse, say that. Ditto for their conjunction.
There is also the problem of using a great philosopher's name to label a principle that the philosopher may not even have held. Analytic philosophers are notorious for being lousy historians. Not all of them, of course, but the run-of-the-mill. If Sommers is right, Leibniz was a traditional logician who did not think of identity as a relation as Frege and Russell do. (p. 127) Accordingly, 'a = b' as this formula is understood in modern predicate logic does not occur in Leibniz.