The real question is “Plating on what”?
Some materials will take gold easily, some need a strike layer of
copper, or a barrier layer of nickel first.
Brass wants nickel first, to keep the brass from oxidizing through
the gold, and there are some things (like titanium) that won’t bond
to gold directly, so they want something like copper there first
that they will bond to, and then you put the gold on that.
It depends on what you’re trying to plate to. (and take this with a
grain of salt: I haven’t done much plating in years, other than
nickel for my tools every so often.)