The PIP system is very difficult to navigate, if you are thinking about it then do get advice, the CAB gives help online, Benefits and Work website is great but you have to pay for a years' subscription to access it. Unfortunately, just getting the forms and filling them in yourself honestly without any advice on the particular aspects of your condition that DWP need to know could easily result in a very low points score.
If you have historic and ongoing medical evidence to support your claim, you should be okay through the process, but again, do use the guidelines.
Claimants are advised to provide medical evidence, but this is becoming a bit of a lottery in itself because some doctors only provide the absolute minimum of information.
e.g. someone wants medical evidence to say how their condition affects them and hampers their ability to do daily tasks, but the medic in question, often their GP or consultant will only provide a letter which has to be paid for confirming the patient has the named condition. They will not state how that condition affects that patient, which is understandable really because they don't see the patient in daily living circumstances.
Blue Badges - the criteria which the badges cover have been extended to include more than just physical mobility, but each council has different rules. Ours will not renew a BB unless the recipient is receiving the enhanced rate of PIP mobility. We had a bit of a moment trying to renew my relative's BB for the third or fourth time because although they'd received indefinite DLA, they were changing to PIP and waiting for Tribunal during the time the BB was up for renewal, so couldn't meet the 'you must have enhanced PIP Mobility' criteria. Fortunately, the council decided to carry out their own assessment of relative's mobility, despite relative having had a BB from them for several years, and the Council's Physio assessed them as much less mobile than the ATOS assessor had, so that provided more evidence for Tribunal and the BB was renewed in the meantime.
PIP isn't impossible to get, it's just difficult, the whole process is very intense and demoralising. DWP can be less than helpful, e.g. telling you to reply within a month of the date of their letter, but you look art that date on the day it arrived, you find you've received it after 2 weeks have passed then find there's a bank holiday coming up which makes your theoretical month to reply to them more like just over a week.
LittleDragonGirl there's a separate thread about that rumour.