What did you find hard to understand about double entry accounting? Seems pretty straightforward. Every transaction affects at least two accounts, and the total debits must equal the total credits. I can't imagine how introducing graph theory simplifies it, although I trust there are interesting insights none-the-less.

I think it explains the "why" of double entry accounting. Since it is used to track flows of money, a graph representation is a natural representation (just not the only one and not necessarily the most useful for day to day operations).