The problem to create an optimum patch file is a problem getting harder with growing file size quite fast. BinPatch applies many different techniques to reduce the patch size to something around of 60% of what concurrent software achieves.
But with growing file sizes, the effort required for all these optimizations may become too much. This is why we chose to introduce a system of optimization levels. The default is "-8" which includes all reasonable optimizations. The maximum optimization is enabled with "-9" and includes some very much performance costing analysis that only rarely gets you better results, most often you get the same results as with "-8".
The other levels "-7" down to "-0" provide a way to trade more and more efficiency to gain speed at creating the patch file. While "-7" might give you quite good results still, "-0" will attempt to be as fast as possible, leaving out most any chance to be efficient in terms of patch size.