Even if you’re getting them to rez ICE and then trashing it with cutlery, are you saying that the corp is not re-installing ICE back on that server?
Put another way, when you make a run on the remote (or RnD or wherever), do you ever make non-cutlery runs against servers that have derezzed ICE? If you do, it’s to your benefit to use blackmail. In the case that you plan to come back in and use cutlery later, it’s even more in your benefit to use blackmail now, since you’ll only have to break that ICE one time instead of twice.
Basically, if you’re ever making non-cutlery runs (and you should be, I think), then Blackmail is a great card and will save you credits/cards from your hand and allow you to use them later.
Some people build Val with Blackmail as the most important card; I don’t think it’s that great. However, I can’t imagine a good Val build that isn’t better with Blackmail in it. As I say, if you’re not sure what to cut just cut your least important economy cards (though there’s probably even worse cards lying around that you could cut); you’ll make the savings up on the run.
This is misleading, I think. Blackmail isn’t only useful when there’s no rezzed ICE on the server; it’s useful when there’s any unrezzed ICE on the server. Let’s say you attack the remote early without blackmail in order to clear out an econ asset or a Caprice or whatever. They get to rez an Eli over it and yes, that Eli is safe from being blocked out via blackmail. However, when they go to drop a Tollbooth on that server, you’d very happily play Blackmail on that server and break Eli the normal way, no? Blackmail isn’t only a sniping tool; it’s a cost reduction tool