If a gun is safe as is, it is a waste of money to sleeve either the bores or chambers. Cyril Adams shot sleeved guns because ten gauges are not allowed in the games he plays. I will also guess that Cyril paid about a tenth of the price of the gun in question. The Scott in the first post is ridiculously overpriced.
Sleeving is a good way to "rescue" guns which have barrels that are no longer "safe as is". Whether from accident, honing to the point that wall thickness is insufficient, etc. In Europe, the process requires that the gun be submitted to the proofhouse of the country in question--very typical in Great Britain, less common in other European countries--for reproof. Which means that you now have a gun that's been tested with the barrels as they now are, not as they were when the gun was new. And old guns that aren't sleeved may have had a fair amount of metal removed from the barrels over the course of their long lives. Thus they may now be out of proof because of excessive bore diameter, or dangerous because of thin walls. You don't have either of those concerns with a sleeved gun. There is reason for concern, however, over how the gun balances and handles post-sleeving. An old gun that hasn't been tampered with and is still in good condition will always be worth more than a sleeved gun. But there comes a point at which--either due to barrel wall thickness approaching .020 or so, or out of proof due to bore diameter--that a sleeved gun can represent equal or greater value than one in original condition. Depending on just how original that condition may be.
