A QuickBooks file becoming too large can lead to performance issues, such as slow loading times, difficulty opening the file, or even errors when trying to save or back up data. Common causes for large QuickBooks files include excess transaction history, numerous lists (customers, vendors, items), or lack of regular data maintenance (like condensing old data). To manage file size, consider archiving or deleting unnecessary transactions, using the "Condense Data" feature, or upgrading hardware for better performance. Regular file maintenance and optimizing QuickBooks settings can help prevent slowdowns and ensure smoother operation.