Some years ago most of the major brand oil companies decided to reduce the amount of seal conditioners and swellers used in their High Mileage oils to comply with API specs for newer cars. So if you have a 10 year old can of an High Mileage oil and compare it with the same current product, it has less in the way of seal swellers in particular and in reality are less effective at reducing oil consumption (If it's caused by valve guide oil seals and not bad rings), or oil leaks. Obviously that move was good for the sales of High Mileage oils and it was good in profit terms because most of the base stocks used are just cheap dino or cheap HC synthetics.
I don't think any oil company is making a GTL or Group 4 synthoil High Mileage oil, or even making an 0w40 High Mileage (Might be wrong about that), so although High Mileage oils do have their uses, they have been a step in the wrong direction if your vehicle has a turbo or you like doing extended OCI's in particular.
PS: If you have an oil dripper or burner that is beyond economic repair, first of all find out what is causing the problem, as it might be fuel contamination or thin oil use. If the rings are bad, then there is not a lot you can do other than keep the revs low and experiment with extra AW additives, fuel additives (If it's a stuck oil control ring issue) and even Italian tunes ups to burn out the Carbon.
If the valve guide oil seals are bad and you don't need an 0w, then if the problem is not too bad, an High Mileage oil might be of use if it has the correct specs (USE THE OIL FINDER PAGE and owners manual), otherwise try a major brand stop leal additive as the good ones are far more effective than High Mileage oils.
Oil leaks that are beyond economic repair can be reduced or even stopped by using both a stop leak additive AND a thicker oil, BUT be careful as thicker oils can increase upper cylinder wear rates due to slower flow rates. Moving up one grade never seems to cause any real issues unless the oil flow is already restricted by sludge or varnish.
Finally make sure the crank case vent system is working, cos if it blocks, the oil drip or burn rate can go into orbit!
PPS: Just to clarify one point, seal conditioners soften oil seals which helps them work, BUT it also increases the rate at which a new or good oil seal wears out if the oil contains the levels used in High Mileage oils, so in reality there is not much difference between a sweller and a conditioner.