Base64 is a format in which binary data (1’s and 0’s) is represented by simple characters only.
What’s the use?
By using only 64 characters known to be widely supported on almost any platform, it’s preventing all kinds of problems caused by special characters.
Depending on the platform or protocol some characters are considered special and need to be handled differently.
For example e-mailing binary files in Base64 format is almost never a problem.