Difference between [[ -n $VAR ]] and [[ $VAR ]] in Bash

Question

Is there a difference between these two options in Bash:

# 1
if [[ "$VAR" ]]; then 

#2
if [[ -n "$VAR" ]]; then 

If not, are there situations that really require the -n option?

Answer 1

Since [[ is smarter than test about variables there are essentially no situations that require -n.

$ foo=-n
$ [[ $foo ]] ; echo $?
0
$ [[ -n ]] ; echo $?
bash: unexpected argument `]]' to conditional unary operator
bash: syntax error near `]]'
$ foo="-z bar"
$ [[ $foo ]] ; echo $?
0
$ [ $foo ] ; echo $?
1