I have been considering just having a SSD in my new gaming computer and having a USB 3.0 HDD to store my movies on. With a portable HDD, it will allow me to take it to friends place etc. I am wondering if it will be faster and more worthwhile. I do not have enough to spend on the HDD when first building the computer so if i do get an internal it will be install after a few months.
I see no reason, other than you may run out of space on the SSD if you don't buy a big enough one.
USB3.0 is fast enough to not seriously bottleneck a HDD. But you'll want to get a 7200RPM drive in an enclosure, versus buying an external. A pre-built external will give you a pretty weak 5400RPM drive.