When we have a user input task why do we use start form

Start forms are great because they don't actually start the process. This means if the user closes the tab, they don't have a task lingering in their task tab and no process has started. Typically if the user is initiating the action such as clicking on a related action, start forms are best. If the user needs to be assigned a task, then the User Input task is best. I almost always prefer start forms.