I had to think about the best answer to your question for a couple days, because, truth be told, I actually don't do much testing specifically for performance, but I am constantly thinking about it. I think the simplest answer is "that's the only way I know how to be".
From optimizing the 3D model, to packing UV sheets, to programming, I work like I'm still living in the 2000's, when every line of code and every polygon counted. It actually makes me rather upset when I see the default MSFS 2024 aircraft, which waste polygons like graphics cards grow on trees. In some aircraft, over half the recommended polygon budget is wasted on literally inaccessible engine geometry. (In case you've ever wondered why MSFS 2024 runs so poorly) Even in MSFS 2020, there would be knobs in the cockpit with 10x more polygons than they needed.
The same goes for textures and code. I am constantly looking for algorithms and shortcuts that I can use to speed up code execution. If I've done my job right, you shouldn't be able to notice. I saw some people who were shocked that my Starship avionics suite was "only" 30,000 lines of code, and my tablet interface is "only" 5,000". All I can say is that this wasn't by accident. I'm quite proud of my optimizations, but that's probably where I should leave it, in case anyone begs to differ. There is always more that can be done, but I try to strike a healthy balance. Excellent question!