Never. 100% included in lease subsidized for whatever silly reason. Sure, I pay manhattan rent ($1800/month) but I pay that with my normal income already. Mining is 100% free for me..

I currently pay ZERO. In manhattan! No, my parents aren't paying for it or anything.. I just have no utility bills!

There are a lot of "legit" reasons why they do not mine with their own product.

1. They have capital investments, and that means they have capital investors that need returns at specific risk profiles. Building then using $10 million worth of machines is a HUGE risk to have for a company. Yes, it might work out, but it's not nearly as liquid as preselling machines for a price that reflects only a 7%-10% return when factoring the increase in difficulty rating and lowering of block sizes (to 25). They are probably locking in 40% on building and selling these things, and their investors are practically already paid for their (relatively) risky investment into a new venture.

2. "Competition risk": If you have the largest farm in the world, someone is going to try and copy/beat you. If that happens, the value of the BTC mined, as well as the ASIC's made would fall due to supply increases. By pre-selling these machines and not using them, they lock in their profits at a respectable level and have to put no more work into it.

3. Energy/Equipment/Land: These costs could be prohibiting them from producing a decent profit on the ASIC platform. I can bet you that their profits/KWH are higher just building and selling than mining and selling coins

4. Insurance: You have $10 million of breakable, unprotected ASIC chips clustered together to mine BTC. One bad accident can destroy the entire investment, and it is also probably very expensive to insure such items.

5. Taxes: If you sell ASIC platforms via bitcoins, they can be transferred anywhere in the world before being converted into currency. That's a great way to deposit funds into tax shelters to me (if you do it right). Plus, there is obfuscation of profits on items sold for any international currency (They can write off "losses").

6. Exchange rate risk: Just like gold, bitcoins are basically a reserve currency. They can be instantly traded into any other currency without having to worry about Forex/international shifts of the host. Imagine selling $10 million usd of ASIC's to find out that the currency of your home company has just gained 20% over the dollar overnight. In order to repatriate your income, you have to take an automatic 20% cut off the top... or wait until the possibility that the currency regains value. That's a huge risk, and all international companies have to take this into account if they are to be successful.

You can make guesses, but I believe people use the "days destroyed" as the most used way to see unique transactions.