What are good use cases for building custom MCP connectors (e.g., QuickBooks, ramp, digits) with Claude?

One member built an MCP that connects Claude directly to QuickBooks using the accountant profile, allowing switching between clients and posting journal entries. Main use cases include quick data lookups (e.g., a client's net income for a given month) and pile-of-transaction reviews. The more developed workflow involves building workpapers in Excel that Claude reads, checks against prior-month ending GL balances, does the reconciliation work in the workpaper, and then uploads journal entries to QuickBooks—effectively acting as a 'robot staff accountant.' Similar MCP connectors are in progress for ramp and digits, and a Claude skill was shared on the AI Lab site (under 'builds') so others can attempt to build their own MCP, though it's described as still a work in progress and results may vary for other users.