No sparge can be pretty good but there's a practical limit of brewhouse efficiency due to grain absorption.

Yes this is my experience. Apologies in advance for metric measures - on my last brew I mashed 3.7kg grain in 21 litres of water. One litre of wort is lost in absorption for every 1 kg of grain. So maximum I can get from the no sparge mash is 17.7 litres wort from my 21 litres liquor, i.e. theoretical maximum 84% efficiency assuming no other losses. I don't think 90% is possible.

In practice I get about 75-80%. I might get a few % more with a sparge, but the cost saving from that few % extra is negligible. My time is worth more than 50 cents (or thereabouts) an hour, so I'd rather just use a bit more malt to compensate and skip the mash.