Oh phones it is really all about the screen and battery life for most people.
CPUs right now are fast enough for majority of people. Of course there are users that need the fastest CPU, GPU and so on and others that need the lowest possible power draw.
On phones it's even more ridiculous. Your fancy "octacore" processor isn't (it's 4 big beefy powerful cores and 4 lower power cores).
Even if you could power all 8 cores, you won't do it for more than a couple of minutes because the heat output of those cores would cause thermal limiting once they hit max junction temperature (approx. 125C, after that, the P-N junctions on the semiconductors break down).
In the end, after doing all the calculations, in free air, a quad core is basically maxed out with two cores going full tilt and the other two at half load. In free air. In an enclosed environment like a phone where you have PoP memory (memory is attached on top of the CPU to save space and get better reliability by not having high-speed lines routed on PCB), your max speed is limited to dual core or less.
ARMs have a typical power consumption of 1mW/MHz - it can change, but in general that's the relation. A quad core 2.5GHz chip means roughly 10W (octacore roughly 20W), not counting GPU or other cores on the chip. Thermal resistance is generally high so you limit fast.
Heck, on a Snapdragon board, we need 4 core processing without thermal limiters which meant instead of running the CPUs at 2.2GHz, we fixed their frequencies at... 1GHz. This is with open-air cooling and thermal pads to conduct heat away and it still gets mighty toasty.
It's one reason why Apple pretty much sticks with dual core - dual core processors don't need to thermally limit even going full tilt, and when your quadcore or octacore is going to thermally limit to dual core anyways, it doesn't make sense.
Specs may matter, but a lot of them are really just BS numbers in the end because you can get that performance in theory only.