At minimum it will help to show one more empty seat, plus as long as your intention from today on is to never contribute financially, then thats good.
I'm not going to hound you for renewing last year, not everyone joins the boycott at the same time. As long as you've joined now, thats what matters.
I personally started boycotting since last January after the defeat at Villa Park, which coincided with news that there won't be any January transfers to bolster our PL survival.