Main benefit is putting pressure on allies, especially the US, to stop sending weapons etc. Israel might not give a fuck but the US does. I think that's why Israel is worried about the whole thing.

Canada's PM Trudeau says that they will abide by the ruling of the ICJ case. Before they didn't want to get the side-eye from big bro US so they mostly want along with their anti-violence but unconditionally pro-Israel stance until recently.

https://www.cbc.ca/news/politics/israel-gaza-genocide-international-court-justice-hague-south-africa-1.7084682

The ICC is also not a UN body and, notably, lacks the membership of the most powerful geopolitical players (the USA, China, Russia, India) as well as much of Asia, the Middle East, and Africa.

It's useless.