Crypsis gets a lot of hate in the runner world. A lot of times, the objection is "it's too expensive!" There is some truth to that claim. On average, Crypsis will cost you a few more credits to break the ice you encounter. (See this useful post). Added to that, you have to spend a click in order to break a piece of ice without losing Crypsis permanently. Depending on the current state of your economy, this equates to 1-4 lost credits for that turn.
What Crypsis lacks in economy, it more than makes up for in utility. Imagine this situation: the game has just begun. The corp plays a face-down card in a remote server, lays a piece of ice on top of it, and takes a credit. Now what? If you run the server, and the corp rezzes an Enigma, and all you have on hand is a Corroder… You're done. The corp is scoring an agenda and there's jack all you can do about it.
Crypsis fills the holes that your other icebreakers leave behind. As long as you have the credits, you're in. No questions asked. Once you've played crypsis and another relevant icebreaker, you can pretty much stack your resources and call it a day. Without Crypsis, you're going to be spending time drawing cards and assembling the perfect rig before making a dent in the corp's ice.
Depending on your opponent, running blind into enemy ice runs the gamut between "not a good idea" and "a game endingingly bad idea." Crypsis softens this blow. As long as you have a decent credit cushion, you can investigate the outermost ice, then jack out if things look dicey. You have the comfort of knowing that no matter what the corp throws at you, you can handle it. No other icebreaker (besides Wyrm, which is even more expensive, outside some exotic combos) can provide that safety.
Any given runner deck should be stressing resources first. Without credits, you can't install, can't break ice, and can't ditch tags. Runners are much more dependent on credits than the corporation, which can get away with a minimal economy if it can intimidate the runner into not making a run. For the most part, rezzing ice is a one time affair, while breaking that ice is something a runner might do 2-3 times. All that said, you should have enough resources to fund Crypsis. You should think of Crypsis as your baseline icebreaker. Anything less expensive than that is just gravy.
Crypsis is especially useful to Anarchs and runners splashing Djinn - Crypsis also happens to be a virus, which means that Noise can use him to mill a card, and Djinn can tutor for him (for those not into magic: the gathering lingo, "splashing" means to include a card outside the type that you might ordinarily take (in this case, to use influence to purchase a card from outside your faction), "mill" means "to put a card from your deck into your discard," and "tutor" means "to search your deck for a card and put it in your hand").
Crypsis is just good. He's generally useful like having extra credits is useful. You don't know when you'll need him, but he's good to have around, just in case. And if you finally do assemble the perfect rig, with the most efficient breakers? Just get rid of him, or pawn him to Aesop. Crypsis is one of the foundation cards for successful running.