In order to look at the potential disadvantages we will have to look at three sections:
Cryptocurrency - is a digital asset designed to work as a medium of exchange that uses strong cryptography to secure financial transactions. Bitcoin - by far the biggest and most popular cryptocurrency which is almost 70% of the total valuation of cryptocurrency market. Bitcoin price movements affect all of the other cryptos. Blockchain - is the technology behind most cryptocurrencies. It's a database which is growing list of records, called blocks, that are linked using cryptography.
4 main Bitcoin Disadvantages
Transaction fees - Bitcoin transaction fees are still relatively high and are currently between $1-$2. At the peak in December 2017 fees reached almost $40 and the peak this year was almost $6.
Transaction speed - it currently takes between 10-20 minutes and at the peak in 2018 took several days.
Lost wallets - Most people are not ready to take full responsibility for their assets and are not able to manage their private keys securely. A lot of Bitcoin have been lost or stolen.
User friendliness - It is difficult to use Bitcoin - opening wallets, buying Bitcoins, sending Bitcoins are all tricky for new users.
Transaction fees and speed - The fees and speed are deeply connected to the volume meaning more transactions will increase both. Lightning Network is the obvious solution here and it works creating channels between users where it conduct numerous transactions outside of the main blockchain and then record them as a single one. It needs to be widely adopted however.
Lost wallets - Centralised wallets are the solution here but there is no solution for truly decentralised wallets where users are their own bank...