Is Tuna Good for cats? Or dangerous? And why?

First off, I never give my cat people food because I really rather stay on the safe side because I would be heartbroken if she got sick.
Another thing to keep in mind is that every cat is different and might have a different reaction if they eat tuna intended for humans in an excessive amount.
I feel that in this situation it is better to be safe than sorry so I would just stick to store bought cat food brands.