Pine knots and fat wood are two different things. Out west here, I'll cut into a dead, standing Pinyon and this yellow, fat like junk starts to run all over the saw. Really, it looks like liquid beef fat. That's when I grab a can and try to get all that I can. After the tree is cut, I mark it with a red 'X', and let it sit for an hour or so till the fat has somewhat solidified. I use the wood from these trees for firestarting and it's like putting kerosene to a match! The stuff in the can I soak cotton balls, or better yet, dryer lint in and use it for starting fires as well. If you find some of this fatwood, use very small pieces as this stuff burns really, really hot.
BTW, if you go to the dollar store and buy a container of hair pomade, you can roll the cotton balls in that stuff and it burns just as good as vaseline.