▻http://blog.perrygeo.net/2010/02/18/lazy-#raster-processing-with-#gdal-vrts
So what’s the advantage to doing it the #vrt way? They both produce exactly the same output raster. The Lazy VRT method delays all the computationally-intensive processing until it is actually required. The intermediate files, instead of containing the raw raster output of the actual computation, are XML files which contain the instructions to get the desired output. Additionaly, the VRT method produces only small intermediate xml files instead of having a potentially huge data management (...)