In short, the assessment should be made every time you have a change in income or deduction that TAKS is not automatically notified of. For example, if you have a B-income, which is not paid via the tax withholding system, or if you have other significant changes to your income or deductions.
However, if you only receive A-income (which is taxed at source via the tax withholding system) and no other form of income, you don't need to do a preliminary tax assessment. You also don't need to do a preliminary tax assessment if you receive B-income and there have been no changes to a previously registered preliminary tax assessment. In this case, the net result for the current year is automatically carried forward as income used for B-tax predictions in the following year.