Should you buy bitcoin? If not, why not? And if so, how much?

The answer is probably none if your investing aim is to finance basic things like retirement or build a buffer in case you lose your job. But there are some good reasons to invest in bitcoin or other cryptocurrencies, and your reasoning determines how much you should own. Here are some target allocations based on investing goals:

You want some extra risk to spice things up

Investing in bitcoin is speculative. It may surge or it may crash. There are many risky assets out there but bitcoin is exciting because it’s the next big thing (maybe). It adds an element of risk to your portfolio, and sometimes risk can pay off.

Some argue bitcoin is valuable because it is uncorrelated with the stock market, so it adds some diversification and reduces risk. There are reasons to be skeptical of this argument. A reliable measure of correlation takes decades of data, and bitcoin has only been around since 2009. Like the US stock market, bitcoin has generally climbed since then, but it’s also fallen. We can’t know if bitcoin really can hedge stock market risk until stocks experience a meaningful and sustained fall. Investing in crypto for diversification’s sake is purely speculative at this stage.

Ideal portfolio allocation: 5% to 10%, depending on how much risk you can stomach

You fear a world where everything falls apart but we still have lots of computing power

Bitcoin might be valuable if the dollar collapses or there’s severe inflation. There may indeed be some value diversifying your currency holdings, especially if you plan to live abroad one day. But you can get this benefit with a lot less risk by holding a different government-backed currency. Of course, there always exists the extreme tail risk that civilization will collapse and all government-backed currencies will be worth only the paper they’re printed on. In that case, bitcoin may be our primary currency. A bitcoin-backed economy would still require good internet service, though, and it is not clear that will be available when we are living through something that resembles the Hunger Games.

Ideal portfolio allocation: 0%, because you should save your money for therapy (and canned goods)

You are really into privacy or want to do something illicit

The other main crypto advantage is privacy. You can conduct your transactions with total privacy, unlike with credit cards. Some people really care about privacy. And if that’s your preference, the risk associated with crypto is the price you pay for anonymity. But be mindful of the cost: Vendors on the dark web sometimes complain that bitcoin volatility can wipe out their profits.

Ideal portfolio allocation: 30% to 40%, depending on the volume of your transactions

Someone is blackmailing you or you want to be prepared for such a thing

The relative anonymity bitcoin offers also has a dark side. It is how criminals often do business. If you are a victim of a cyber attack, hackers often demand ransom in bitcoin. If you must pay up, having some bitcoin handy could be useful. It can act as insurance against a criminal attack, which in an increasingly connected world, is not so rare.

Ideal portfolio allocation: 1% to 5%, depending on how likely you think it is you’ll be attacked

A version of this essay first appeared in Private Key, Quartz’s premium newsletter about the chaotic world of crypto. Sign up for a free two-week trial here, and enter code “privatekey20off” for 20% off your membership.