Using mobile, i received a page with a big face of the author with blah about him surrounded by all sorts of big "login with" overlays and advertisement. Obviously, i jumped to conclusions too quickly as my second attempt after reading your comment presented a slick & clean page with relevant information. ( And no half of the screen filling signup / login overlays ) Hence the "apologies" in the message above.

Regarding your inquiry; because it allows for the original author to do mutations and calculations on (your) data carried or distributed by untrusted third parties. This way someone could for example provide updates while being at less risk. Various asymmetries between the amount of data dumped and the amount of resulted output could also be helpful in certain niche scenarios.