Please, please search for this subject before starting yet another thread where all the same people are going to say all the same things all over again.
You don't even have to use the search function. Just go to the WN forum and scroll through the threads. There has to be at least 4 recent threads about this.
It's really really tired.
WN tacitly allows seat saving and unless it's extremely egregious or ends up in a fight the cabin crew will not intervene.