I have short legs, carried huge and had SPD. By 6 months my bump was a couple of cms from the steering wheel and my pelvis could no longer cope with much open movement.
I must have started using P&C spaces around then because from 36 weeks I could no longer sit behind the steering wheel with any hope of reaching the pedals to drive safely.
I couldn't bend forwards to move the seat so not suitable to ask anyone else to manouver the car because it would be too awkward to re-find the optimum driving position of just reaching the pedals and leaning back enough to get a large baby in his olympic swimming pool in while still being able to see over the bonnet.
Absolutely no way to get in via another door if someone did not allow me the full opening of my door. Getting in through the fully open drivers door was tough enough.
My final supermarket trip was at 34 weeks when my pelvis was burning in agony with no chance of effective pain relief, so no, I was not wasting valuable footsteps by my old trick of parking in the unpopular corner and walking.
During months 6-8 of pregnancy (I couldn't leave the house independently after week 36) my trips out were based very much on parking the absolute closest I reasonably could to the door and minimum walking required.
Without P&C spaces I would have been near housebound for months.
In pregnancy 2, it was pretty much a moot point as DS1 was nearly always with me. However I did have to ask at his swimming lessond if I could use a disabled space if P&C wasn't avaliable (which it frequently wasn't as the toddler lessons had more than toddlers than spaces) as I simply couldn't safely manage my crutches, kit for two and a tantrumy toddler (particularly when tired after the lesson) across from the far end of the carpark. Also my pelvis could not do uphill at that point. My mobility and a hard winter had already severely constrained a lot of our ability to go out and get him active, so I wasn't rushing to waste months of swimming lessons if possible.
I remember staggering into ASDA on the crutches at 38 weeks and being offered a mobility scooter, a tempting offer, but I was quite happy to overexert myself into labour by the vigourous exercise of heaving myself around a few aisles by that stage 
If supply is abundant, I still use P&C now they are in primary school as DS1 has dyspraxia and does not have great control over a heavy car door. Obivously only when they are with me, and I can get a lot of errands done when they are in school so it's not that often. Ironically DS2 is easier to get in and out of a tighter space. I will often park further away in a quieter area if I can.