The Trial Balance is a statement of ledger account balances as on a particular instance.
The trial balance is prepared to check/ensure the arithmetical accuracy of accounting. Preparation of Trial Balance is not an act that forms a part of the activities involved in the regular accounting cycle. Final Accounting can be completed without the preparation of the Trial Balance also.
The trial balance is generally prepared at a time when all the ledger accounts are balanced like at the end of the accounting period. Theoretically, the trial balance can be prepared as and when needed. In this mechanised (computerised) accounting systems, trial balance is a statement that can be automatically derived as and when needed.