That was how Christianity was spread rapidly. That was one of the reasons why it gave the early believers such a zeal that they were able to withstand the greatest of persecutions. When John the Baptist was in prison, he had doubts that Jesus was the Messiah. All of these miracles Jesus pointed to as signs that he was the Messiah. And when Christianity was to be established, those signs were given.
Tongues represent a sign.
Tongues are not given for the believers edification. In 1 Corinthians 14, Paul admonishes teaching and preaching instead over speaking in tongues. Paul states that he who speaks in tongues is not really speaking for communication , he is not really speaking to edify . He is speaking to God, because only God understands what he is saying. This is sarcastic speech.