Depends on the horse and what you want to do with it. You can't ride papers.
You need to ask yourself if the papers add value to you for your purpose.
I can get on a TWH and ride it a couple laps around a field , and look at its shape and know if it is pure bred enough for me, I also refuse to give the TWHBEA a penny of my money either by registering or attending any of their shows. My mare was registered but I wont ever transfer into my name.
Currently I am shopping for an Endurance Arabian. Registration of the horse and parents are important to me. Beyond basic confirmation I can't tell if horse will make a good endurance prospect. I would choose to stack the deck by looking at bloodline. Yeh I am sure Secretariat bred some dud offspring, but if you wanted to win a race and you had to pick between Secretariat's son, and Old Bob who would you choose ?