Bitcoin block hashing protocol is constructed in such a way that it allows to artificially craft, prepare and reuse some data, gaining 20% mining performance boost. Technical details: http://www.mit.edu/~jlrubin/public/pdfs/Asicboost.pdf.
I used to think of SHA-256 computation and bitcoin block header preparation as of separate tasks, why would you mix them? Well, if you economically incentivized — you would, https://twitter.com/BitMEXResearch/status/102528357130354278.
And an interesting consequence: if some proposal is preventing this performance boost (even as a side-effect), you are incentivized to block the proposal, https://medium.com/@WhalePanda/asicboost-the-reason-why-bitmain-blocked-segwit-901fd346ee9f.