What would happen if you received an audit notice from the IRS for your personal or business taxes? Would you freak out and figure you are going to owe all this tax? Or are you confortable with what the auditor will find when your documents are reviewed? The second situation is obviously better; there is still loss of time and there may be some costs if your tax preparer helps you organize and also goes to the audit for you, but at least your stress level is lower.
It is always best to set up all your tax documents as if you are going to get audited, even if the chance is small. If everything is organized, things tend to go smoother than if there is a wave of activity trying to get things at the last minute. One of the advantages of online access to bank statements, credit cards and online billpay is that it is much easier to gather documents. Keep this in mind when you are getting your taxes ready to be prepared and put everything together at that time, then store it all together after your taxes are prepared.
Advance document prep can save you headaches later on.