What are some use cases for worker threads? Initially I thought there must be loads, but when I considered that XHR is asynchronous anyway, and that Worker thre

What are some use cases for worker threads? Initially I thought there must be loads, but when I considered that XHR is asynchronous anyway, and that Worker threads don't have access to the DOM... I guess it would be good if you wanted to use your visitors CPU in the background for password cracking or for the various distributed network stuff like SETI. But what practical benefits do web workers provide for normal web development?