I have actually been experimenting against responsive web lately, partly influenced by bettermotherfuckingwebsite.com (don't worry it's a CSS site)
Responsive web was jaw dropping when it first started but now it's become extremely common. Do people really need to do several different designs for phone, tablet, desktop?
A lot of major sites like Reddit do very well without responsive. And it wouldn't work for something like Stack Overflow because their user base are desktop people who prioritize low friction access.
It takes a long time to load and a long time to build. So most people should really rethink whether they need all this.