AFAIK Nathaniel is essentially correct. Additionally to splitting rattan though, these long handled knives are used for carving wood. Not only does the long handle allow the blade to be driven with the shoulder or belly using the weight and power of the torso, but the massive blade reduces chatter/vibration/wiggle and gives stability to the cut.
On the other hand, SE Asia often shows a close kinship between fighting and work forms and Alan Maisey's highly decorated example is interesting. On an even longer handle, still often curved, there are cutting spears much like this, though they lack the widened butt for pushing against.
I've been drooling over this item, but buying others......
