What is the difference between using the Samsung phone speaker in vehicle vs bluetooth earpiece

[acsurfer]

What is the difference between using the Samsung galaxy S4 speaker in vehicle vs bluetooth earpiece?

If I have mounted the phone to the phone holder, when a call comes in I can press the [speaker] key and chat while I am driving correct?

Why do people need to use a bluetooth earpiece?

 

[anon(632115)]

I guess not everyone has a phone holder in their car. I wouldn't dream of putting one in mine even if my car didn't have BT. I think the earpieces look ridiculous, personally