AutoIndent is an option for Cell which specifies whether automatic indentation should be done at the beginning of a new line after an explicit return character is entered.
In entering a Mathematica expression the amount of indentation inserted is determined by the settings for the LineIndent and LineIndentMaxFraction options.
If or \[NewLine] is used, tabs for indentation will explicitly be inserted into the internal structure of the object representing the contents of the cell.
If \[IndentingNewLine] is used, only this character will be inserted, and indentation will be redone each time the expression is output.
or \[NewLine] is used, tabs for indentation will explicitly be inserted into the internal structure of the object representing the contents of the cell. 
