We can ignore it for the discussion, but the importance of the nuclear threshhold in politics and war is enormous!
Can tactical nukes win a battle that would otherwise be lost? Possibly, yes. But one needs to consider what will happen to your own troops in the area. Nukes are horribly imprecise. One should apply the correct amount of force to destroy a target. Consider an armored column. Yes, it'd be a juicy target for a 1 kt nuke. It could also be destroyed by an aircraft like the A-10, by artillery, or by JDAM types of iron bombs.
Everyone's opinion is different. Consider that STRATEGIC nuclear weapons hold an enemy hostage... "If your armored attack succeeds and Pakistan is going to fall, we WILL lash out with our arsenal and obliterate two dozen major cities. Do you really want to continue your attack?" This works when you have a rational enemy, and despite what people here say
both Pakistan and India are rational. So are the USA, Russia, China, and the other nuclear powers.
I'd say the threat of strategic nuclear attack in response to a devastating conventional invasion is more forceful than tactically nuking the invading forces themselves... and it is much easier to control, and less likely to be accidentally triggered.
So in your scenario, I'd suggest a "message" be sent.... "Stand down, back off, or we WILL use our strategic arsenal." If the message instead was a 1 kiloton tactical nuke over an armored column, the only message that'd send would be "We've crossed the nuclear line... go ahead and retaliate with your own nukes."
It's a difficult question that's been debated for decades.