It doesn't literally mean that, of course one is not better off dying.
My Grandpa had a triple bypass in his 60's to save his life, the miracle of modern science he said at the time, gave him another 28 years.
Unfortunately about 10 years later everything else began to fail, to the point he couldn't do the simple things he enjoyed, like reading. He had a few minor strokes, so he couldn't play his piano anymore because he couldn't remember what came next. In his last decade he used to wake up and say "bugger I'm still here" It was sad to see that,
The point that is being made is that you don't want to be in a position where you're alive but have no quality of life, particularly if your'e not all that old.