QuickBooks is a very date sensitive program. All transactions and reports are dated. QuickBooks automatically applies a date to these. When you do something in QuickBooks, you need to make sure you are entering the correct date.
If you write a check for the 1st of the month, but it cleared the bank on the last day of the prior month, you will have a hard time reconciling the bank. QuickBooks lets you clear the transaction, but your monthly reports will not match the bank reconciliation. Therefore, you need to date your checks for when you are actually handing them out.
Another issue we might see is when a payroll check gets handed out early. The check might be dated for the 1st, but given to the employee early, and the bank cashes it early. When this happens, the tax liabilities become off as well as the bank. If this happens during end/beginning of a quarter, it will have a major impact on the way the quarterly reports are created.
Finally, QuickBooks pulls all reports by dates. If you enter the incorrect date, then you will have a chance of running incorrect reports. If this happens at the end/beginning of the year, there might be tax implications. Also, this can become costly if the Accountant/Bookkeeper has to spend extra time tracking all of the errors down and correcting them.
Pay attention to the date you are using for everything!