That’s not really a solid argument. Blocking is likely implemented as a very tiny piece of what is already very likely a massive table join operation. Computationally, it’s likely to have as much an impact on their compute costs as the floor mats in your car have on fuel efficiency.
Everyone already sees different content. It’s an inherent part of Twitter. It’s not a static site where everyone sees the same thing. You see the tweets of who you’re following, and don’t see tweets of those you’ve muted. All that filtering is happening at the server level. Any new tweets or edited tweets or deleted tweets change that content too, which is happening potentially hundreds of times a second for some users.
Anyway, caching would be implemented after a query for what tweets the user sees is performed to reduce network traffic between a browser and the Twitter servers. There’s some memoization that can be done at the server level, but the blocking feature is likely to have almost no impact on that given the fundamental functionality of Twitter.
Just to reinforce your point, the difference between a cheap running shoe and an expensive running shoe is incredible. When I first started running a few years ago, I was using a very old pair of running shoes I’ve had for a long time. I’ve since been sticking with the New Balance Fresh Foam X 880s (because I have very wide feet and NB seems like the only brand that actually makes their best running shoes in 4E) and it’s like running on a cloud.
And then there’s also the Garmin watch that cost $300 (that I’m now stupidly considering upgrading to the new $600 Forerunner 965), the $120 HRM Pro chest strap, the $3000 Nordic Track x22i for indoor runs I got lightly used on Craigslist for a steal at $900, etc.
And then there’s the races where you’re spending $40, $50, $100+ depending on whether it’s a 5K or 10K or half-marathon. And good running clothes are pricey too.