help in 8B10B coding..

I am doing a project on high speed link transceiver. I have a block called 8B10B encoder. I read the article in wiki about it , but i couldn't understand exactly why its is used.

The method is used in most high speed serial data transmissions. By recoding each data byte to a 10 bit sequence, you get these features:
- clock recovery is possible because level transitions occur at least after 4 bit times
- the bitstream is DC-free and can be AC coupled
- special characters allow data synchronisation