Why do MP3 files use Synchsafe Integers?

I started reading mp3-files in c++.

All went well until I read the specs of the ID3-Tag. There is some information in the ID3v2-Header about its size stored in so-called Synchsafe Integers. That is a four-byte integer where the most significant bit of each byte is set to zero.

I found out how to convert it to an ordinary integer, but I cannot stop asking myself why an integer value is stored in such an unnecessarily complicated way.

I hope there is someone who can tell me why it is stored this way.