Saturated fats have all sorts of uses biologically.
You have to get your calories (ie raw energy) from somewhere. If you limit saturated fat to 10% then what's left for the other 90% is (roughly speaking) unsaturated fat, simple sugars, carbohydrates (ie complex sugars), and protein. In terms of long term habits converting protein to calories is probably not a great choice for your health. If you decide to go for complex carbohydrates over various oils then vegetables that provide those are a good option.
My go-to source for nutrition information is Understanding Nutrition by Whitney and Rolfes.
Or do I want to live longer?
They aren't necessarily mutually exclusive, but different actions could result in different outcomes for each.
For nearly everyone, this isn't impactful to their life. Only their vanity
I'm not saying that ketosis has this kind of an effect, but rather that eating or not eating some other things might. Eg vitamin K2. The body is be able to make vitamin K2, but we might have stronger bones and teeth, and a healthier cardiovascular system, if we get extra K2 from an external source.
