Not having one has done nothing but complicate things for me. Except for this one instance.
But what is a CPF? It is a number that is assigned to each person in Brazil and used mostly for commercial and financial purposes. It seems like you need one for everything. In order to use a pay-as-you-go phone, you must first register it with your CPF number. If you are going to make payments on something, they will ask for your number. This allows them to check and make sure that you are someone who is in good standing with all of your other payments. The national database is online and open to everyone. After you plug in the number, it tells you the situation of the person's CPF - whether it is normal or "irregular". People probably end up going through this process of setting up payments often, because everything down here can be bought in 6 or 12 payments. Or you can pay cash and get a significant discount. We're not just talking about making payments on houses and cars, but about shoes, clothes, and furniture.
But the one time it came in handy not to have a CPF number was when I bought a fridge and washer (everyone basically uses clotheslines instead of dryers here). I checked the prices earlier in the day. I had already withdrawn the maximum limit from the ATM machines and was still slightly short, but I decided to go back to the store anyway. A different sales lady helped me and I told her about the price the other lady had negotiated for me. I assumed it should be an easy process to just pay the bulk of it then and then come back the next day and pay the remaining bit. But that would qualify as doing "payments", so she asked for my CPF number. Since I didn't have a CPF number for payments, nor sufficient cash, she went to the manager and came back, offering a significantly lower price. But even with all the money in my wallet and the change in my pocket, I was lacking about R$20 ($9 American). So she went back again and negotiated it down to the exact amount I had in my wallet. I left the store feeling like I had gotten a steal. But I could never orchestrate something like that. Only God could.
Until I get some more documents straightened out, I can't get a CPF. But thankfully, it was easier for my wife to get one, since she is a foreigner. She has no obligation to the military or obligation to vote (voting is mandatory here). It seems like there is never an end to dealing with documents. I guess that is just part of life here.