The thing is on the medical evidence as some other posters have said - many GPs/consultants don't KNOW how it impacts you on each descriptor.
Like it's not their job to write reports saying how you dress, or eat food - it's their job to diagnose you and provide the needed care. And when you have a long-term incurable condition you often don't have up to date reports to submit which is frustrating as they seem to want lots of evidence dated recently.
I also had previous consultants I'd seen refuse to put in reports when I asked. For example my pain consultant replied 'just use the last letter I sent you' which was one tiny paragraph basically saying what medication I was on, nothing more and my prescriptions would have told them that. He certainly wouldn't take the time to write something helpful.
Having said that I've just transferred from DLA to PIP. I've been absolutely dreading it for six years waiting for the letter, and it actually went well for me although it took awhile. I submitted my forms early November, and I only got the result a few weeks ago now. I paid for a couple of reports to be done so I had some new things to submit. They did an on-paper assessment and gave me the on-going award, which is such a bloody relief.
But there is so much wrong in the system. Even now having been awarded the highest rates when I read my on-paper assessment there was so much wrong. For example they wrote that because I had been in pain rehabilitation recently it showed I could meet new people and socialise. First, the rehab was 2012 - is that recent?! Secondly being admitted to hospital for a very painful and difficult time isn't a fucking party, and shouldn't be used to show I can socialise for gods sake!
And I had one hell of time getting DLA in the first place - I was treated like a criminal and I found the whole thing hard to get over it was so awful.