1. For me it's about using the best option available within reason, recognizing that the best CPU TIM is not the best GPU TIM. And by within reason, I include Cost, Time and Money.
Which one ... I see many folks invest $90 in a cooler only to waste any advantage it provided by losing that advantage with a poor TIM choice. Given the risk, with other peoples money, I tend to avoid the liquid metal options. That and the fact that I haven't hit a "thermal wall" on a build since 2013. The voltage wall gets in the way before the thermal wall becomes an issue. So, in short, can not justify the risk, as minute as it may be, since heat isn't getting in the way of the OC. Performance wise, Grizzly Ktyonaut would be my choice but until recently, it's been $20+ and carried be few vendors always requiring another visit by the UPS man. So for the last dozen years or so, it's been Shin Etsu G751 which has the same thermal properties of AS5 but w/o AS5's capacitance and curing issues. With Kryonaut now available on newegg, if in stock will likely use more often.
https://archive.benchmarkreviews.co...k=view&id=150&Itemid=62&limit=1&limitstart=12
For GPU, I prefer a more workable TIM, or better said, one which maintains its viscosity once out of the tube. Here I use Gelid Extreme
2. I been using both Id say over a dozen years
3. As for application methods, it varies by surface. Unlike most, I tend to use different methods for different coolers / surfaces and follow follow manufacturer's written instructions
CPUs -
https://benchmarkreviews.com/206/best-thermal-paste-application-methods/
GPUs - Step 3
https://www.ekwb.com/shop/EK-IM/EK-IM-3831109868522.pdf
VRMS / Mem Step 4 -
https://www.ekwb.com/shop/EK-IM/EK-IM-3831109868522.pdf
4. As to why, for the CPU, Shin Etsu is $4 and is equal or better than just about any non liquid metal product on the market. It's easy to apply and provides consistent results. However, it tends to lose it's workability after long exposure to air so is not suitable for GFX cards where you are applying TIM to 20+ surfaces some of which are on the opposite side of the card and also the backplate. The ittle oar shaped tool is great for applyoing TIM to individual VRMs w/o making a mess. Wouldn't dare applying LM here.