It's really frustrating how much the web, software, and computers in general are being gimped for everyone just to support the "mobile" segment of the market.
Sometimes I try to squeeze more battery time from my old laptop, and I look for processes hogging the cpu. Invariably I see Firefox consuming 30-40% cpus and I have to hunt down those misbihaving tabs that, even idle, keep the cpu awake.
The reality is that today saving power matters everywhere. On mobile and laptops means a longer lasting battery and/or lighter device; on a desktop and laptop it means a quieter machine; on the datacenter, power usage is probably the most important cost today.
Even on desktops or when laptops are plugged in we should concern ourselves with power usage. If something can be optimized for power usage, it should be.