Use it anywhere where scalability and performance are required, especially if newer SAP version has been implemented.
The mode users will use it, the better - otherwise, the pricing policy could spoil the ROI. Very good integration possibilities, with other standard enterprise applications. Support of various data resources, incl. XML, OLAP etc. including the ability to connect to JAVA, MS Sharepoint, MS Office and .NET applications.
The programmer community around SAP BO is HUGE. It is quite certain, that the problem you have has already been solved by someone else. It requires a little digging in discussions, but the help is mostly available. You definitely cannot start small with SAP BO. It feels too costly,