It’s symbolic in that Trump started his campaign from Trump Towers, and it’s such a significant physical structure, and representative of all things Trump. It’s his castle and brand, amongst other things, and provides a measure of safety and favorable logistics, plus- it puts Trump and his VP pick, at the doorstep of all of the major media outlets in NY. It (also) doesn’t broadcast his pick ahead of time, by being at or near their home turf, except- for Christie, next door in NJ.
I think Trump was going to make the announcement from Trump Towers, no matter the distance, or closeness, it lies, from the home of his pending pick. In other words, I don’t think it is a given that it’s Christie, because the announcement is taking place in NY. It could, on the other hand, very well be Christie.
A pundit stated that the VP pick accounts for 1% of the vote. That may be statistically true- but it is not a hard fact every single time, because I am SURE Sarah Palin accounted for far more than 1% of McCain’s votes.