What is difference between JavaScript Remoting and

The <apex:actionFunction> component also lets you call controller action methods through JavaScript.
In general, <apex:actionFunction> is easier to use and requires less code, while JavaScript remoting offers more flexibility.

Here are some specific differences between the two.
The <apex:actionFunction> tag:

 1. lets you specify rerender targets
 2. submits the form
 3. doesn’t require you to write any JavaScript
JavaScript remoting:

1. lets you pass parameters
2. provides a callback
3. requires you to write some JavaScript