This is best answered by telling you why I made it.
I used to do my monthly budget in Excel.
This was very nice for a geek like me because it is easy to add up lists of income and expenses.
I could even have it give me a yearly summary without too much work.
But it became very difficult when I realized after doing an entire year's worth of monthly budgets that I wanted to add one more expense starting all the way back in February.
So I had to go add it to each individual month.
It was a tedious and time-consuming job, and I thought 'wow, it really shouldn't be too hard to make a computer do this for me.'
So I made a program that lets me add and remove expenses, income and savings wherever I want.
Plus it is smart enough to ask me if I want a particular change to happen for the month I'm editing only, or for the entire year, or just start with the current month and go to the end of the year.
(This is very helpful for bills that don't exist until half way through the year, or if you have a regular payment that ends part way through the year.)
Finally, I like to get a picture of how my money is being used.
That way I can think about where I can save money, or see on a larger scale where I'm using most of my money.
So there I added a "summary" screen. This lets you choose a range of months within the year and see where all your money is coming from and going to.