Low tension rings put less pressure on the cylinder wall and create less friction. That is good for a high performance application where engines are routinely torn down for inspection. They seem to loose their tension after about 80-100K in a daily driver. The oil rails let oil past when they stick in the ring grooves of the piston and and the engine starts to use oil.
Some car companies are using the low tension rings because it makes for a very efficient air pump when it's new and you get better fuel economy and you can raise your fleet economy numbers.

Gus