Take a gander at this...

[FlamedToACrisp]

Why do people say, "What's good for the goose is good for the gander," to mean... ooh... just about any random thing, from what I can make out?
The phrase is, "Sauce for the goose is sauce for the gander."

I don’t understand why the sauce thing is particularly important?

Doesn’t it just mean if it’s acceptable for one thing, it’s acceptable for another?

Preparing to be enlightened!

I'm not sure, OP, whether you're querying if it's 'sauce' or 'good' or the actual meaning .

Agree with Puppy... if it's good enough for X then it's good enough for Y.

I always understood the saying to be: 'what's sauce for the goose is sauce for the gander'.

It definitely isn't 'what's good for the goose is good for the gander' although, I've heard that used many times.

So many of these saying seem to have been changed over recent years.

One that I find particularly annoying is the saying: 'the proof of the pudding is in the eating' having been changed to 'the proof's in the pudding'. It doesn't have the same meaning and it makes no sense.