In this discussion I will assume that God exists, unique and posses the absolute power. I know this is a lot to assume but I will express my thoughts about these stuff in another time..
I have two points of view for this question.
First of all, this is not really an issue for God if she/he posses the absolute power! Lets explain this with an example. If we would have seen Bill Gates giving 200 dollars to a beggar, the first thing come to our mind would be it is not a big deal for him. Unless it is given from a normal citizen it could only be interesting as a magazine new. Because we know that it is not a bit for Bill Gates. Just like this example, creating a billions of galaxies is not even an issue for God Almighty (if it ever exists..). She/he has all the power and this is just an easy peasy thing to do..
Another thing is to wipe out the possibility of underestimating the power of God by the arrogant human race (This is my thought. It may be wrong of course! I felt like I write on behalf of God, but I am not. Please consider that God may have a different opinion on that 🙂 ) For example, once my friend claimed to me that human body is not perfect. In fact, he said it is far to be perfect. For instance our eyes.. According to him, they could have much better design and creation so that we could have seen larger angles and longer distances in a more decent way. I agree with him that our eyes could have been more sophisticated but there is no border of that idea. I told him that if our eyes would have seen 360 degree with a very large radius then you might still argue that they are not perfect. You could have said they are not sending fire balls! There is no end of this argument. And even with your eyes current capacity you are claiming it is subpar. There is no point to argue with people who think our body system is not perfect (in its own). Arrogant people can even undervalue a system that works 60 70 years 24hours/7 days! Human body has very similar cycle in a micro way with the universe. God creates billions of galaxies which are similar systems in the macro way for our human bodies. Therefore, all those billions of galaxies can be interpreted, so to speak, to bring mankind into line and saying that before underrating anything God created, we should think more!
Is it only for us?
I highly doubt it! Why should we so special in the universe? In an ant point of view, it might think they are important, but the earth spinning without even noticing ants. We don’t even think of them for 1 min in our whole life. And just like this, the universe has a cycle in which we are extremely unimportant and small in it!