What do banks do with the data they collect from you?

So I’ve had bank accounts since I was allowed to (since 16, which was over 14 years ago). Since I have accounts with over 5 banks, I probably provided them with a ton of data. I’ve called them and they told me that they use this data to “improve my experience”, not sure what that means. Should I be worried about the amount of data I’m distributing by opening accounts with different banks?

accounts bank banks called collect data data i experience privacy ton