It's also helpful when building any kind of system that deals with money. That system will inevitably integrate with some more elaborate ERP/Sales/other system, and for that it's quite helpful to know about the principles of accounting, even for the developers.

(Especially helpful if you live in countries like Germany, where the tax authorities can pretty quickly finish your company if you can't account for every single cent. But I think also in the US (SOX etc) this might be helpful.)