There are two reason why I think this:
a) Political advertising on social media is very hard to police as you can create huge amount of versions of each ad and target very different audiences.
b) Political advertising at volume favors the richest campaigns with the largest amount of knowledge about their targets.
By blanket removing political advertising from these platforms more focus would have to be made for more traditional forms of political work (door to door etc) and thus a slower more deliberate political climate.
It is by no means panacea but a good start.
Norway has always forbiden political TV-advertising, something that I think has helped the debate stay a bit less polarized, though that has changed with the advent of Facebook and it's ilk.