TN's do not allow for immigrant intent....Translation: If you have immigrant intent, or if the officer can show that he beleives you have immigrant intent at the time when you are attempting to enter in TN status, then he can deny you TN status.
What happens after you entered using TN status, is a little different....
As one court put it, “there is a great difference between wanting to stay and intending to stay and proof of a desire to stay is not proof of an intent to stay.”
Choy v. Barber, 279 F.2d 642, 645-46 (9th Cir. 1960)
After you get your TN, and THEN you suddenly get the desire to have immigrant intent by marrying a USC and filing an I-130/I-485, you are no longer eligible for a new TN. This action in-and-of-itself does not cancel or void your curent TN as long as you are still in the US at this point. It does however make you inadmissable in TN status. Inamissable does not mean you should get deported. It simply means you cannot enter the US in TN status, this includes your current TN status.
To rectify this problem, the only thing you need is an Advance Parole the next time you enter the US. With an Advance Parole you would not be entering in TN status, and therefor you would NOT be inadmissable.... You would be admissible in "AOS Pending" status.
Many people have gone through AOS starting in TN status through marriage, DV, and employment sponsorships. It hasn't "haunted" any of them AFAIK. I've never heard of anyone other than Geemoney's lawyer requesting that a waiver be filed. I suppose it can't hurt, but I'm also challenging its worth.
Geemoney, did your lawyer state what types of problems you could encounter if you didn't file the waiver? I ask, since I have not heard of any issues that a waiver like this could prevent.