Basically, there are two types of laser engraving machines. The ones that guide the laser beam with a set of mirrors, and the cnc version. The first one is way faster, but less constant in quality. The cnc machine is slower, but much more constant in quality, and with the possibility to blow air and keep the textile from burning.
I have been working with these machines for many years now and most of the time know exactly what the result will be. But every material reacts differently and I still do trials at the start of every day in a factory, and am often surprised by some of the outcome. PVC melts or burns, microfiber velvets can be engraved very cleanly, in linen it takes part of the colour of the fibres away, etcetera.
As laser engraving is a digitally controlled technique, and thus spills hardly any starting-up material, it is very interesting in my opinion to use it on part of a yardage and afterwards combine the untreated and the engraved version in one interior.