The 4K60 S+ is more substantial than Elgato's previous external cards, the HD60 S and HD60 S+, and includes an SD card slot so that you can record footage without first connecting the device to a PC. With support for HEVC encoding, running out of space shouldn't be too much of an issue -- as long as you have a decently sized card. That said, if you do end up using a PC to take advantage of a bigger hard drive, you'll also get access to Elgato's software, which has a couple of handy features. For example, one allows you to retroactively capture footage if you forgot to hit the record button, while another lets you record microphone audio through a separate channel.
All that versatility and functionality comes at a cost, however. At $400, the 4K60 S+ is the most expensive capture card Elgato currently offers. You can get much of the same functionality with the company's more affordable 4K60 Pro ($330), but that requires giving up a PCIe slot inside your computer, making it not ideal for every setup. Of course, for streamers who already plan to buy one of the next-generation consoles at launch, $400 is probably a small price to pay to get the best possible streaming experience.