The origin mate saves you two mates, every time you use it.
It’s a feature that you don’t easily run into. Someone else has to point it out to you.
Today, that someone else is me.
SOLIDWORKS always marks the first assembly component as fixed, unless you do not drag the model into your assembly, but just click the green checkmark!
I always remove this property (right-click > Float) for this component. To me, it looks like a lazy person just left it there.
Then I add three mates: Front Plane to Front Plane, Top Plane to Top Plane and Right Plane to Right Plane. Which feels like a chore.
There is a hidden option when you create a standard Coincident mate and it only reveals itself when you select two origins. It doesn’t even work with regular points.
You can see two versions of the mate window below. The version on the left is the one you have seen a gazillion times. The one on the right shows the hidden option.
You can make the two points coincident just like you can do with any other two points, or you can align all three axes and make all three planes of the components coincident.
Keeping that checkbox checked will save you from adding two extra mates. Who can say no to that?
The previous example showed how you can use this feature for adding the first part to an assembly.
The origin mate works for any combination of models though.
Mating two origins is great when you design parts with a common origin. That way you can get ten parts (or assemblies) fully constrained with only ten mates.
No, there is no difference in performance between three coincident mates and an origin mate.
Underwater they are exactly the same, so there is no reason not to use the origin mate!