Defining Dimension Usage Relationships

I’ve got one fact table linked to 5 dimension tables.
If I add another fact table and join the new fact table to one of the original dimension tables.
My question I want to link my fact table to another dimension table. so why do I need to drag and drop a link from the fact table to the dimension table. When I can just use the usage dimension.
So basically what purpose does creating a link in the data souse view achieve when I can just use the dimension usage.