I did a paper on this in college a long time ago. From what I was able to discern, it was an experiment to see if a firestorm could be created: first wave was high explosives followed by a second wave that were incendiary. The idea was to blast the wood frame buildings apart, then set them on fire. The huge fire would then create fantastic winds which would feed oxygen into the conflagration, somewhat like what oxygen does for acetylene. Having said that, the Germans had it coming in a BIG way. There was a large ball bearing plant there as well, IIRC.
Hadn't that already been proven in 1943 with the fire-bombing of Hamburg?