It's simple really. It's called 'a point of diminishing return' and every program or game or app has it. It's affected by more than just the cpu. It's affected by the game code, by the gpu, by the monitor.
There's exactly no difference to your perception on a 144Hz monitor to a game running at 200fps or 500fps. The point of diminishing return is the minimum fps beyond refresh of the monitor. Most ppl have a extremely difficult time differentiating between 100Hz and 150Hz, but no issues with 30-60.
With most games, a cpu faster than 3.2GHz is all that's required to start reaching that point. Cpus slower than that start showing more obvious results, lack of fps, that ppl can see. But thats in most games, not all. If you take games like Ashes of The Singularity, that's extremely hard on the cpu in general, so a higher speed, newer gen cpu is warranted. Matching core to core, a i9 9700 shows massive differences to an FX8 series.
Physical life expectancy of a cpu is well over 20 years. I've got a PentiumII 350MHz that's seen a 400MHz OC since day 1 and still runs perfectly fine. That said, both of you are incorrect. There's no answer as to whether OC will reduce lifespan because the lifespan is an unknown. For all we know, it could be 50 years before catastrophic failure rates render it useless, so even cutting that in quarter is still far beyond any useful usage. A 12yr old cpu is useless for age appropriate software. Don't assume voltage and cooling are the only factors, amperage is the other half of power and when voltages are minimal, amperage is maximum to maintain the power levels. Lower voltages prevent bleeding between the nodes, maintaining stability, but amperage affects how hard those nodes get slammed when transferring the voltage.
Overclocking is for anyone, everyone, everybody uses it. Turbo is a factory set OC. Nobody runs their pc at base speed, turbo off. Manual OC or even the stupid software included OC is nothing more than a user's extension of turbo settings. It's used in cpus, gpus (boost clocks), ram (xmp profiles). Nobody buys 3200MHz ram and runs it at ddr4 default rates of 2133MHz. Even vendors recognise that fact, every listing above cpu set memory controller speeds (2133, 2400, 2666) is xxx (OC) in the ram listing.
So yes, OC is for everyone, How Much OC is a personal decision.
Oh, which Corsair H150i? There's 2. The original release was great. The ML fans were strong, quiet and got great temps out of that rad. Then that release was discontinued shortly after, replaced in favor of the RGB version for a popularity contest with other RGB AIO's. The latest version sucks in comparison to the original. The RGB fans now used are half the ability of the originals, something had to give in order to make room in the motor housing for the RGB pcb and wiring needs. Bad move for performance, but Corsair relies more on brand recognition than actual performance standings for sales. Why buy a plain 360mm aio and buy $90 worth of rgb fans when you can buy the whole thing far cheaper.