I am not quite sure what this form is about (AFTER reading this form's instruction from the irs.gov site).

quote from the 1041-T form, Purpose of the form:

"A trust or, for its final tax year, a decedent’s estate may elect
under section 643(g) to have any part of its estimated tax
payments (but not income tax withheld) treated as made by a
beneficiary or beneficiaries. The fiduciary files Form 1041-T to
make the election. Once made, the election is irrevocable"

does irrevocable mean just for this year or forever?
if I don't plan on making estimate tax payments, do I have to file this form?

if I DO plan on making estimate tax payments, and I didn't file this form.
what will happen when I file my fiduciary tax return and the beneficiary's tax return next year?
will I lose something? I just don't get it.

This is my first year filing a fiduciary return that was created in 2011.
it have a rental income and need to depreciate the rental.
I do expect to have a income in the thousands after deductions and depreciation. and there is no other income.