Consistency between accounting, bookkeeping, tax preparation, and tax planning brings clarity to the financial side of your operation. All parties will know what has been done and why, and there will be no doubt about whether any tasks were completed correctly. Filing tax returns, preparing monthly financials, generating reports, and other processes become more efficient.
To be clear, these are not DIY functions. DIY is too risky when it comes to financials. While all data and activity will always be accessible and visible, the actual work should be done by a professional to ensure accuracy and compliance. And a licensed CPA will be able to offer guidance and bring a level of knowledge to the table that a non-CPA cannot.