I have renovated houses professionally off and on for over a decade. If you pull them out and they look ok, 90% of the time they will bend and be a PITA when you are trying to drive them with a hammer. I always save handmade nails, they are very cool and much tougher.
Roofing nails for sure you can salvage, but a 3 1/2 framing spike no way, especially if the wood has gotten wet.
I was thinking about the phrase "tough as nails". Nails are very easy to bend, but very hard to break. Screws are hardened and brittle so you may as well just hammer the joint and break the screw when doing demo. If there is more than one nail in a joint, you are going to have to hammer the bejeezus out of it and often times ruin whatever you are trying to separate. There is a reason there are so many different types of nail pullers!
I reuse screws all the time. It is a good practice to collect them as you remove them, as almost anything is hard enough to damage a wood floor if you step on it with boots. You can tell right away if they are bent, and you can reuse them sometimes even if they are bent. 3 1/2 or 4 construction screws are more expensive than nails, and have a higher chance of successful salvage, so you might as well try to save them. One can never have enough screws or nails, as you know.
I have Knipex carpenter's pincers too, I've removed many a nail in my day. The worst are the aluminum siding nails, they are soft as butter.
