Question about Seagate Expansion Portable

Of course you can, why shouldn't you? The hard disk behaves like any other storage medium on the PC.
But remember... Accessing an external 2.5 inch hard disk via USB is slower than accessing an internal 3.5 inch or even an SSD. Personally, I would always go for internal disks when gaming. External ones only for data backups or any kind of outsourcing if necessary.