It doesn’t have to be “for” anything. It doesn’t have to be any good. It doesn’t have to even see the light of day. But it does have to be written. Because it will prepare the ground for the next thing. Because you will feel better for doing it. And because practice makes better. (Not perfect, never perfect. Just better.)
Write a line, a poem, a letter, a limerick. Not because you have to, or because you should. Because it’s fun.