I use Schwalbe tires as well and I do use liners. I think that combo is a real winner. I had only half a dozen punctures during my entire 5-year around the world tour by bike, no joke! And 3/4 of them were within 1 month in northern India.
Why so many in India? Because during the winter, Indian women go out in the bush, cut branches of acacia and drag them on the road all the way back home to use them as fuel. And believe me, the thorns from acacia in India are scary, they are so hard and so strong that I had a couple of them pierce my Teva sandals all the way through into my foot!
I use Slime liners
but Mr Tuffy
are even better (and pricier, of course). The edges are not as sharp and they are lighter. It is hard to tell if they are more efficient.
Some people complain about the weight but I'd really rather not have to worry about and deal with flat tires and would prefer to carry a couple extra ounces.
Once in a while I inspect my tires and dig away all sorts of nasty stuff (pieces of glass, thorns, metal, wire, you name it).
It takes a little bit more time to change the tube, though, because you have to put the liner back into place.