Is it better to buy hay? I think it all depends on what you are doing and the amount you are doing and where you are doing it. Every region has its own set of resources which can be managed to keep the feed costs down and make the cows pay their way. The profitable producers identify their unfair advantages and utilize them but not everyone is in this to make a profit. Many just own cattle for tax reasons or just for the sake of owning cattle.
I think its interesting to see how others do things in different areas and this sometimes gives me ideas to try. What really intrigues me is how some can make false premises for themselves and actually believe them to be true and base their management decisions on these things in spite of all the information refuting their "facts".
To me, my main priority is reducing inputs both time and money. I'm a meat producer and not a seedstock producer so my main concern is getting each and every cow to wean a live calf. Calf growth rates are a low priority with me because when you look at the total herd's weaning weight the indivdual's growth rate has little meaning if each cow doesn't have a live calf by its side. I would much rather buy hay but buying hay only assures you that you will probably be buying filler that you have to supplement or not having hay or being gouged when things get tight. Supplementation costs money which then runs up the cost of your hay and if omitted only leads to reduced calving rates.
The only way I have found you can assure yourself of a high calving percentage and a low input cost is to grow the best forage you can grow and utilize this in the most efficient manner possible. How you utilize the forage is different from farm to farm or region to region. And I am also not saying you should fertilize every square foot of you property as this only leads to poor utilization. Its all a balancing act which is complicated by the whims of mother nature and its left to you to come up with what truly works in your location.
Bottom line is I think you need to be honest with yourself and use real facts and toss out the sharp pencil and use one with a little blunt to it to be sure you are operating on conservative figures and not fine tuned projections based on a perfect world. But this is only if you truly want to make a profit. If you don't, and all you want is some pretty fat cattle to grace your fields then pour the feed to them in tubs, bunks or the bag and I assure you they will be pretty and slick and will eat everything can afford to pour in front of them .... and then some.
I also think people should chart out their forage production by field and month. This will identify the weak months and then you can look at how best to fill these gaps in the most economical manner possible. Doing this will allow you to see the forest rather than fixating on the trees. JMO