i baled 118 4x4 round bales off 8 acres last year. That's 3,540.00 @ 30 / roll value in 1 cutting.
That land is 10-14k / ac land. lets say you pulled 200 for the year. that's 6k in hay. Every 2 years you'll pay for an acre. 8 acres would take 16 years to pay for in hay. Not bad when considering how much the land is valued.
Now to the understock so you don't have to make hay theory. In KY I fed hay around Xmas every single year. They were back to grazing on March 20th, every year. I had 3 months of hay feeding, around 600-800 round bales. If I understocked and fed stockpiled grass, I'm guessing I'd have to cut my herd size in almost half. What would you do with all the grass in the warm months? buy stockers? You can't gain enough weight in that time on grass alone to make them even worth it. 800 bales @ 30 each is 24,000 dollars. My hay equipment cost me around 10k. What about fertilizer and seed!?!?!? Well, I unroll my bales where I got the hay. no seed / fertilizer needed. 0 input costs other then fuel.
Anyway you want to spin it it just doesn't make sense.