Try browsing the web on a semi-decent laptop from, say, 2008.
It's a frustrating experience. It is obnoxious how much CPU power modern websites require.
Honestly, back when my PSU died I just did that. Beyond the lack of video decoding support for modern codecs it was perfectly acceptable as a backup machine.
It's worse than that. At least someone would profit off of those bitcoins being mined. Instead we use all of that power to make the dozens of dependencies play nice with one another.