TN-extension of stay/ i-129 form required?

I will be applying for a 3-year TN after Christmas to continue my work in the U.S. with my current employer.
I have been on the TN for quite a few years and I've always submitted a completed i-129 form (Petition for a Nonimmigrant Worker) with my employer's letter. Most of the time I never had a problem, but a couple times I was told it was not necessary (and one time I was scolded for doing so). I'm a bit confused as I have been getting mixed reactions and don't want to raise any red flags or cause any unecessary confusion in my application especially in this uncertain times.

I'd guess I could just have the i-129 form completed just in case and present it to them if they ask.

I don't know what other things I could do to help support my application this time, as I'm worried that USCIS will be more stringent in accepting applications because of the poor U.S. economy.

Thanks!