[AYBABTME]

The latencies stack up for any web page. It's not like "oh this file was served 5ms sooner", it's an accumulation of latencies over all assets, and the interactions, that are required to present an experience to a user.

Also, latency measured at the server is amplified once its received by the browser. And when the user's connection isn't great, all this is worsened. It quickly adds up. In fact, it doesn't "adds" up, it "multiplies" up.

[sjwright]

If you’re serving so many elements that 5-msec-per improvements really accumulate, your problem is page complexity, not marginal latency.

[AYBABTME]

Most pages nowadays are spamming requests to backend services, for business logic or not, that's just reality. Barely any actual real world money making website is going to have < dozen requests per page, and won't need a user initiated page load every few seconds to minutes.