Why is it so important for both men?

This is because it represents everything the two men long for. Their farm is symbolic of a sense of belonging that every character yearns for in this novella. Isolation and lack of place are constant themes throughout this story. Both men are itinerant labourers at the mercy of bosses who hold all the cards. The world is also a dangerous place for a guy like Lennie. Basically a six year old in a man's body, Lennie is vulnerable in the simplest of social interactions. A place of their own might insulate Lennie from this world. More than this, a little farm gives George and Lennie a sense of control in a world where they have absolutely none.