You can't try to give inputs that will lead to desired outputs if you have no free will. You can't try to do anything. You just do exactly what you're programed to do.
If I tell someone not to do something again, then that is an input to their future states whether or not my decision to tell them that was freely chosen or not.
If you go into that situation with the belief that not having free will means that what you do does not matter, and your action as a result is to not tell them, then that will affect their future states too. And so whether or not you have a real, free choice, it is beneficial to act as if free will exist even if you see it as an illusion.
I strongly believe we have no free will. I still get up and work, and try to do as best I can. I believe those choices are not free, but they feel like choices, and they impact my life, so I am happy I act as if they are free.
And so I'll still talk about making choices and trying to do things because of that illusion even though I believe it's all a chain of cause and effect.