What attacks do Guard Up work against?

I'm CB main, but if possible I'd like confirmation from any weapon.

I see some people using Guard Up, and it's been a favorite skill of mine in past games, but after I switched from Rompopo Axe to a more Meta build the only attacks I've not been able to block that I've tried to are grabs, Rey Dau charged railgun, and a specific Ajarakan move where he lifts the ground under you.

What other attacks are effected by each level of Guard Up? And is it worth it to just use 1 or 2 levels if there are certain moves that are effected by just the lower levels?