Naturally, this is most powerful with unconditional AI breakers (that is, AI breakers that when powered up sufficiently can break through any ICE that's not explicitly anti-AI like Swordsman). With such a breaker, System Seizure can save you a ton of money against big servers and a couple credits against smaller two ICE ones. Let's have a look at some of the candidates:
Crypsis. That's right, Crypsis! The traditional flaw of Crypsis is that the costs overall are too high compared to just using something else. This card cuts those costs right down, making Crypsis the most no-frills option for a cheap all-server solution...as long as System Seizure remains up. And therein lies the problem: This probably can't be your primary game plan, and if it's not up then Crypsis is quite lackluster. So you're running it with a bunch of normal breakers to keep costs down, and at that point how much benefit are you really getting?
Faust. Now this is more like it. System Seizure greatly increases Faust's reach, making it far less draining to crack multiple ICE with the famous AI breaker. I think this card will fit well in the Current slot in Faust decks.
Brahman. Only goes in specialize decks, but given how horribly inefficient Brahman's strength boosting is it benefits quite a bit from this card.
Eater. Like Crypsis, but usable.
Overmind. I think Overmind decks will quite like this card. Between using counters to break and System Seizure, you're looking at breaking an entire server for the low, low price of "the highest ICE strength in the server" so long as you have the counters. And an Overmind deck where the Overmind doesn't have enough counters isn't really much of an Overmind deck at all, now is it?
An honorable mention goes to Aghora, which while it can't crack all ICE will generally be targeted at ICE that is expensive to break, which makes a cost saver like this quite welcome.
Finally, it is a 0 cost 1 influence current which means it doubles as a good way to turn off the Corp's current in a deck that wants to use it. This might even make it worth using in cases where the benefit is more marginal.