Question: I wanted to buy a 512GB NVMe SSD and a 1TB Seagate BarraCuda 7200rpm HDD for my new computer but I remembered I have a 2TB USB 3.0 Segate backup plus slim drive laying around in the house.

Would it be better to use that 2TB USB SSD and a 256GB NVMe instead of the initial configuration?

I know that USB 3.0 is 1 Gb/s slower than SATA III but SSDs are also way faster than HDDs.

Answer:512GB NVMe for your OS and applications.
The other drives is all your personal preference. Some, all, or none of them.