It's one of those most important things that matters.
The end user likely won't notice the difference between 4k and 720p. They also aren't likely to notice the transition from one to the other.
The person on the VPN, VoIP call, video conference, video game, etc. will very much notice the congested link, even if it's only a few seconds.
Yes, Netflix video is very efficient, if not the most efficient. They're also one of if not the largest slingers of bits on the Internet. Small changes in usage of such a huge player totally eclipse most other usages on the Internet.
Netflix recommends 25 megs for Ultra HD, while only 5 megs for HD. That's a 5x difference in something people likely won't notice and would make a big difference on the additional VPN, VoIP, video conferencing, etc.