I had to clear out my saved cache recently due to the fact that a certain website would not work any time cookies were made for it, and clearing out my browser's chache was the only solution i found. I already assumed it would remove all of the autofill, and maybe even my saved passwords from the memory (thankfully it didn't delete the passwords themselves), and I thought I would just be able to log back into everything and have it autofill from there. Even with the option turned on in settings, it still doesn't automatically log me in when i load up the page, the autofill is there when i go to manually log in, but for something like youtube it can get irritating, even if it is 3 button clicks.