Even if power use is a minor concern for desktops, it would be good to program with energy consumption in mind :>

Network utilization, CPU usage, memory, disk usage, energy consumption. Lots to focus on...

"Longer battery life" can be restated as: a lower ambient temperature for your room/office; less CPU cooler fan noise; a lower power bill; the ability to pack more servers per rack in a co-lo environment (yes, servers run browsers–headless ones, for spidering/scraping); etc. It can even be restated in terms of extra performance, when you consider technologies like Intel's Turbo Boost.

I would expect that lower power use is highly correlated to low CPU/GPU use, which can be beneficial for other reasons than reducing power use.

Nothing is being "gimped" for the benefit of laptops, and paying attention to power consumption (direct or indirect) benefits pretty much everything.

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.

Electricity isn't free.

Desktop Safari doesn't have a 'power saving mode' and it consumer less power than Chrome. Apparently MS Edge is the same (I don't use Windows so I can't know). These browsers don't have user-visible tradeoffs, they're just more power efficient.

Or is this just a case of Chrome being really really unoptimised and power hungry?

It does a lot more than lower brightness and cap clock speeds, it also disables night-shift and screws with all of the background process and predictive fetching, etc which the OS does.

> So basically, default mode should be battery-saving mode.

The default mode is already a battery-saving one, you can get an impression of a non-battery-saving mode by playing a game continuously, your battery will get run into the ground in 2~3h.

> Am I missing something?

Low Power Mode is not about downclocking the phone and trying to sip power, it's about disabling a number of features which can already be disabled individually, but which (as far as Apple is concerned anyway) most users want/use:

* animated transitions

* automatic mail fetch

* Hey Siri

* background app refresh

* automatic downloads

* wifi association/roaming

* night shift

In essence, LPM makes the smartphone less smart to try and last a bit longer. If these are smarts you don't need, you could disable them all along.