the first pass is usually an algorithmic digest. the human element is required to recognize a subset of all transactions as requiring further analysis. some transactions require special consideration in either tax or reporting contexts. if every accounting system were a relational database, and every entry had multiple foreign keys to every appropriate classification, we could virtually eliminate CPA's. as it stands each accounting system is bespoke and idiosyncratic. some of them record transactions on sheets of paper.
source: dating a CPA