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The only reason I can think of not to use a pile of them as mulch is if you're the sort of person who's always sticking your bare hands into the soil. Seems like it could be scratchy? If you were organized enough to wear gloves (and shoes) that wouldn't matter.
I'd guess they decompose a lot slower than most of what is in your compost bin, so probably that wouldn't be a good idea.
I have both fir cones and Ponderosa cones and I run them through my Debris loader (shredder) and put them in the compost for soil structure. They take about a year or two to break down. Makes a great hotels for worm and salamander families. I usually produce about 6 yards of start that breaks down to 2 yards a year so I compost everything but sticks. I have used them for mulch but they don't hold in the moisture and arent too pretty when shredded. Many different shapes and ugly.