It’s important for the same reason that defining a peanut is important if a person is allergic to peanuts. Peanuts, in that case, need to be defined - because defining things enables us to recognize them, to distinguish a threat from a non-threat - and then the threat needs to be removed from life and, through careful daily effort, kept out. The risk of not defining the threat is that I will die from anaphylaxis.
In my case, I am allergic to lust, and I must define it for the same reason.
There are many tens of thousands of people who have worked lust- and/or sex-addiction recovery programs that have been carefully tested, reviewed, and revised over time - including SA, SAA, and SLAA, for example, and beyond those there are also more general recovery programs (SMART Recovery, Dharma Recovery, etc etc - see this thread: Resources for our recovery) - and there is ample research- and practice-informed literature available from those programs, to help you develop a reliable working definition of lust.
It is up to you and you only to look deep into yourself and pay attention to signs, and seek input from knowledgeable, experienced people to interpret those signs. Then put their input into action, pay attention for signs again, and repeat the consultation process.
What I share here is my personal experience. I tried controlling my body for many years. Control, in my case, included software blocks, accountability software, and many many many different ways to try to control what my eyes could or could not see, or what my hands could or could not do. I tried this for decades, actually. Ultimately I came to the conclusion that it was a fruitless effort. The problem was not caused by anything in my body or by what my body was or was not doing (including what my body was viewing, or what hormones - including dopamine - were being produced in my body), and the solution did not start in my body. The solution had nothing to do with control.
For me, the solution was deeper. It was psychological.