Why should cryptocurrencies be used?

The reasons are many, but they are not trivial. The first reason is certainly so-called disintermediation: those who possess cryptocurrencies in a proprietary wallet, and therefore not in an exchange, can use them at will, without necessarily having to resort to an intermediary, unlike in the case of a bank.
The advantages of disintermediation are often very difficult to notice, for the simple reason that we are so accustomed to using intermediaries to use any service we take for granted. But in the crypto-money sector, the intermediaries are far from obvious.
For example, the first advantage is that you can dispense with banks, you can dispense with the issuer of the credit card or the circuit where you make payments, you can dispense with Paypal, ApplePay, SamsungPay and any other intermediary. However, it will be an irreversible process that we will be received in a short time...
Cryptocurrencies from this point of view are like cash: exchanges can be direct, one to one: without an intermediary. This means that there is not even a commission on the cost of the transaction and, above all, no spending limit if not the balance of the wallet, without prohibition, without control, without territorial barrier, without authorization to request large amounts. And transactions are fast (occur in a few minutes or seconds) and are cheap, free and uncensored.
This advantage may not seem particularly important at first glance, but anyone who has tried to move large amounts of money with fiduciary currencies, especially abroad, knows very well how useful it can be (value date of 7 to 10 days and also high costs that can affect 10-15% for small amounts of money).
The second advantage is decentralization. In reality, not all cryptocurrencies are decentralized, but the most interesting ones are.
The advantage of decentralization is that nobody can touch its assets: a decentralized currency cannot be modified, altered, manipulated or, above all, overvalued.
Even in this case, those who are accustomed to using currencies such as dollars or euros (subject to low but constant inflation) could not understand this advantage immediately, but those who are accustomed to currencies manipulated to the extreme (such as the Venezuelan bolivar), or strongly inflationary (such as the Argentine peso or the Turkish lira), surely already know how useful it can be.
Venezuelans, for example, have already understood this very well and it is no coincidence that they are increasingly changing their bolivars into BTC, DASH and other cryptocurrencies.
Sooner or later, any fiduciary currency can suffer excessive manipulation or inflation, and that's when they realize that decentralization can be a great advantage.

Cryptocurrencies are immune to inflation

The third advantage is the fact that all transactions made with your wallet are tracked perennially and unchangeably, and are also public, making it very easy not only to take into account your own incoming or outgoing transactions, but also, for example, to prove without any doubt that you have made a payment. Everything is done under sunlight, publicly recorded for all eternity.
For example, by using different addresses to receive or send tokens to different people or companies, you can have an irrefutable record of all the transactions that took place over time between two subjects. In addition, since the transactions are public, not only the sender but also the recipient can see the entire history (which is not objectionable).
The fourth advantage, which should not be underestimated, is the deflationary nature of many decentralized cryptocurrencies (mainly Bitcoin), which makes them immune to inflation generated by excess currency issuance and therefore tend to increase in value over time.
In other words, they can also be a good investment, even if nothing and no one can guarantee that we will earn money by investing.
To date, these are the main advantages derived from the use of cryptocurrencies instead of fiduciary currencies. In the future, other advantages are likely to be added, due, on the one hand, to additional technological developments and, on the other hand, to so-called second layers such as Lightning Network, which multiply their innovative potential, allowing a greater number of transactions and with even more limited time.