It's not at all unimportant. It's part of the reason people are upset that they paid for XXXMbps connection but "Only get XXXMbps" throughput.

In most households having a limited single-stream throughput isn't a big deal, but it IS a big deal specifically for things like your 4K streaming. It's VERY difficult to do TRUE sustained 4K streaming over any kind of distance. If your ISP happens to have a Netflix caching box at the local pop you're golden. If you need to traverse any kind of distance across the internet - good luck.

edit: I guess I should've also said, more to the point, it's why gigabit hasn't gotten the legs most people were hoping for. When you look at the per-stream throughput on that site - in general if you have any kind of packet loss you're talking about 10Mbps. Who has 100 different streams in an average household???