Use cases for graph algorithms and graph data structures in finance and banking
There are many use cases of graph theory in Finance industry and it is a very broad question. As Emre said can be used for Fraud Detection, Risk Modelling, Economic Networks etc.

These below links can give you better understanding of different application, please go through for better understanding:


Applications of Graph Theory In Finance
 Graph Theory for Systemic Risk Models 
Graph theory: connections in the market
Analysis of Equity Markets: A Graph Theory Approach
Portfolio Diversification
From Graph Theory to Models of Economic Networks. A Tutorial


Do let me know if you need any additional information.