Do these systems under threat need fortifying?

I'm still learning about PP, there's two systems under threat in the CONTROL tab of PP:

IENPALANG, undermine target met, about 1300 fortifications to reach the fortification target. The system is 64.8LY. Do I understand it correctly that it would be bad if the undermine succeeded? It would cost more CC right? Should this system be fortified?

KANUKET, 43% to undermine and 19% to fortify but it's 105LY.

Before spending any time on these I'd like to make sure it's the right thing to do.