INS is a one-number measurement used by commercial soap makers to quickly compare various blends of fats. This measurement was invented quite some decades ago, so I don't know if it's even still used in commercial soap making anymore.
The "ideal" INS value of 160 is something proposed by handcrafted soap makers, however. That "ideal" is totally unrealistic for me (and I suspect for many other soap makers).
The only way to get the INS that high is to use a lot more coconut (or other "cleansing" fats) than I want to use. There's no way I'm going to make soap like that all in the name of meeting a measurement that someone thinks is "best".
You can use INS as a guide if you want but it is just one number that's kind of ... one dimensional.
For example, a 100% lard recipe and second recipe with a blend of coconut and olive might have the same INS number. Both soaps might behave the same when making and unmolding the soap, but that's only part of the story. The lard soap will last a long time and will produce low amounts of dense long-lived lather. The coconut-olive soap will have a much shorter life in the bath and will produce a generous amount of fluffy lather.
So it doesn't make sense for a handcrafted soap maker to have a strong focus on INS. As an alternative you can evaluate the various fatty acid percentages in a proposed recipe. More numbers to deal with, that's true, but the fatty acid profile will also give you a more nuanced idea about what the soap will be like.
Here's the rest of what I have to say about INS and iodine value:
English: Iodine Number and INS | Soapy Stuff
French translation: L'indice d'iode et le INS | Soapy Stuff