Not necessarily: a byproduct of mining is heat. It's hard to get rid of the heat in large centralized operations. In small operations less so, it may even be useful in some cases.

At some point mining cost will mostly be energy, not hardware. I've recently encountered a weird situation regarding solar electricity production (pretty decentralized in germany, where I live): in certain cases the array produces excess electricity which can neither be used locally nor fed into the grid for profit (due to stupid laws and regulations). Usually what is done in such cases is the electricity is just injected for free to the grid... what a waste economically, right? Well, if you have some cheap asics (so cheap that you can just have them laying around idle if not needed) you can make good use of the excess electricity.