Billing is complicated because getting money in exchange for services is complicated. The company wants to increase pricing complexity, as to better reflect the

Billing is complicated because getting money in exchange for services is complicated. The company wants to increase pricing complexity, as to better reflect their own costs and to better price discriminate, and this runs directly into the problem of trying to express those constraints in the real world. As noted, trying to fit billing into our stupid calendar system is tricky, because the calendar is stupid. Then, if you want plan upgrades/downgrades, you need to do pro-rata adjustments, and the interactions between that and tax/billing periods/etc makes the entire thing a headache. And then you often need to add some way for the sales team to change things on an ad-hoc basis for sales/special negotiations/etc because of course big customers are going to negotiate something special, and that's all custom logic. After that, now the marketing wants referral credits, and then they want promotional periods that interact with customer loyalty, and on and on it goes.