Something which can potentially be VERY important is how you answer the questions.
Always answer in a bad to good format, not a good to bad. The assessors and decision-makers are somewhat notorious for reading the first part, making a note and ignoring the second part.
This DOES NOT mean you have to lie, just be mindful of how you answer something.
To give an example which might clarify this a little, let’s assume you can walk 100 metres, on a good day but on a bad day you struggle with anything over a few steps, you should phrase your answer as “Not very far at all, only a few metres although I can, on good days, walk substantially further”. Either way is telling the same story but if the person reading it takes the shortcut I referred to before, the difference is between them recording “I can walk 100 metres” and “I can only walk a few metres”.
If you have to go to a face-to-face assessment (probably will unless your condition is particularly bad and well documented) be sure to answer any questions there the same way, bad to good.
Again I am NOT suggesting lying or being dishonest in any way, shape or form, just be aware of how things can be misinterpreted if you aren’t careful.
I can’t 100% state that it was a deciding factor or not, but when I first applied for PIP I answered the questions in a good-to-bad style, I was turned down flat, fought it, and after the year-long appeal process ended up on Low care and High mobility. I have since had to re-apply and this time I did the bad-to-good and got the same Low/High combo without having to go through any appeal process. My condition had not deteriorated (or improved) in any notable way between the two applications although they WERE almost 3 years apart so it may well be down to a change in practices at the DWP.
"Man is born in freedom, but he soon becomes a slave, in cages of convention, from the cradle, to the grave."