1) My driver's license costs $150 to renew once every 5 years - I don't want to split that into 60 monthly allocations of $2.50 and end up having over $100 sitting in my account for an expense that's still not due for over a year. I just want a tool that knows what expenses are coming up over the next 3/6/12 months and let me know if it thinks I'm going to overdraw my account. $150 is actually really easy to scrape together when you have 6 months notice that you're going to be short.
2) I spend $100 on public transport every 2nd Thursday because I get paid every 2nd Thursday. That means either $200/month or $300/month depending how many Thursdays fall inside the calendar month, and whether they're actually the Thursdays that I get paid on. Having a monthly budget that allocates $217/month on public transport (because that's the monthly average) makes me set aside $17 most months unnecessarily, or possibly leave me short $83 and unable to get to work if I spend the remainder.