This low efficiency = better beer stuff is just complete bullshit. A well designed lauter tun and and properly conducted mash and lauter should be yeilding in the order of 90% efficiency, and if it does - thats a good thing not a bad thing.
High efficiency isn't bad... Oversparging is bad, if you get your high efficiency without oversparging, then there is nothing, absolutely nothing wrong with it.
If your system isn't well designed and/or your technique is bad - you will get poor efficiency, and if you then flog it up to high levels by sparging more aggressively, thats where the quality issues lie.
I sit in a room all day long at work, and i watch live graphs of run-off gravity/ph/tint etc scrolling as 20 brews a day go through our system. You can see the run-off gravity drop as a sparge proceeds, you can see it bottom out as the useful part of sparging reaches its end and and its essentially just water coming through, you can see the gravity suddenly & sharply rise as the polyphenols and other rubbish start to come through. With a iittle experience you dont even need the graphs, you go downstairs and watch the siteglass on the outlet of the lauter grant and you can see it... It gets lighter and lighter in colour, then it stops being clear and amber and changes to a cloudy yellow green murk. Thats the bottom. Guess where you cut the run-off?
And if you cut the runoff before the muck comes through, you dont have quality implications.
Now fair enough, at home you dont have live monitoring and graphs to tell you exactly when to cut your gravity... But then again at work we are getting efficiency in the 95% range and cut-off gravities of 1-2 plato. At home you build in some safety and cut off at 2-3plato and your efficiency will be lower. Great, sensible, thats what you should do. Someone earlier said they taste their wort and it goes from sweet to watery to husky.... Cut it off before the husky point, establish what gravity that happens at and stop a little before. Thats all sensible - but if your system is well made, then you're still going to be getting efficiency in the high 80s or near.
So the idea of cutting off at a point where your mash/lauter efficiency was at 75% is either an admission that your system isn't all that good, you are talking to someone who you suspect has a system isn't all that good - or its just an absolutely over the top safety margin. Its the brewing equivalent of always driving at 40 in a 60 zone. Sure - you're never, ever going to lose control and drive into a telegraph pole, but then again, its not like going at 55 is exactly reckless driving either.
So - if choking your efficiency down to 75 makes you feel better, thats fine, its certainly going to make sure you never experience issues from over sparging. But thats a massivey different thing to thinking that somehow getting a good solid high efficiency is inherrently a bad thing for beer quality. It isn't.
Oh, and if you do decide you want to be quite that cautious - then you need to remember that the object of the game isn't actually to reduce your efficiency... The object is to change your process to avoid any hint of the possible detrimental effects of excessive sparging. So you reduce your sparge, thats the goal - reduced efficiency is simply the result of that step.
So - if you crush your grain more coarsely and that reduces you efficiency. Yu are stil sparging just as much and you have done nothing to address the actual cause of the quality issues you are trying to avoid. You're just throwing money in the bin for nothing.
If you sparge more quickly and this reduces your efficiency - not only are you still sparging just as much and failing to address the actual issue, you are also making it more likely that the fast sparge will expose any design issues in your lauter tun and oversparge sections of your grain bed. So you are not only failing to address the issue that you are trying to address, you are throwing your money in the bin and potentially making things worse.
What you need to do is just crush, mash and lauter in the manner you have spent so much time and effort learning is the "optimum" way to do it. Make it so that if you wanted to, you could easily get 90% efficiency.... Then all you do is stop collecting your wort earlier. Leave behind extract that you could get if you wanted, and in the process leave behind all the bad stuff you belive you might get if you tried to get more. You've used more grain (because your efficiency is lower) so all you're doing is collecting the same amount of extract, in a smaller amount of stronger wort that you believe is of "higher quality". You get your volume by diluting.
Me, I get about 89% efficiency on my home system using what i think is a genuinely high quality process & the only significant change i can envisage happening to my beer by me deliberatly aiming for a lower efficiency, is that it would cost me more to make.