We get most of our eggs from a local farm and quite often we get double yolks. Since the bulk of our baking is cookies, we simply use the double yolk instead of two eggs.

I've only come across such a thing a couple of times - and not recently. It's the total volume of the egg that counts, so wouldn't a double yolk mean less of the white, but not more egg - unless the shells were larger too? Or are the double yolks smaller than normal?

It would likely make the results richer, I think.

The only time I get double yolks is when I buy jumbo eggs, and I only buy those when they are the same price as large eggs, and many times they are the same price, at least lately.

I use the double yolk eggs the same as I do regular eggs, unless I am separating the whites and have a special use for the whites. Two yolks count as two yolks in any case. If using jumbo eggs, I already have extra whites.

I wish recipes called for volume of egg whites instead of the number of eggs to use.

So, function. In a cheesecake the egg is partially for glue adn partially for loft. While the increased fat could have an effect for some things, I think in cheesecake it'll just hang out with the cheese fat, and the liquid volume is more important. You don't mention it mixing up weirdly, so I think the liquid was fine, which it might not be if you'd reduced the number of eggs. There should be, more or less, the same amount of white as for a single yolk egg, though I've seen them where it was mostly just yolks, I think when the yolks were particularly big. If your recipe was for one of the denser kinds of cheesecake, like mostly cream cheese, I doubt you'd be able to tell. For a light baked ricotta cheesecake, if there were less white than normal, it might possibly be a bit heavy. In general, it shouldn't be a big issue in cheesecake.

There are other things where the double yolk might throw off your ratios. If it were more important, you could have removed the extra yolks and weighed the result. If it were significantly less than normal for 4 large eggs (you can look up the numbers online), it would be worth adding the remainder from another egg.

I have my own chickens and often get double yolked eggs. I count them as one large egg and just plop them into whatever I'm cooking/baking. It's worked so far.

Annie