I just finished an explanation to a good question in Intermediate that was quite involved. I had apparently a paren in my post that the new post algorithm doesn't like. So it told me to go Back to my post and guess what -- my text was gone, all 40 lines. No way to get it back, not cached, nothing.
That's beyond VERY annoying, especially when you've written something you decide is worth saving off.
Beware! You may want to write a long post into a local editor first.