What does a tax preparer need from your bookkeeping?
A good preparer needs a reconciled trial balance, year-end bank and loan statements, a fixed asset list with purchase dates and amounts, details of owner transactions, payroll reports, and support for any large or unusual items. When those are ready in January, the return is simple. When they aren't, your preparer either bills you hourly to reconstruct them or files an extension and you wait until October.
Because the person closing your books is a CPA, we prepare the package the way we'd want to receive it. We also catch the things that are easy to miss: personal expenses that need to come out, a vehicle that should be on the depreciation schedule, or an S corp owner whose salary looks unreasonably low.