In my travels I have often seen shell syntax like the following:

[ x"$VAR" != x"value" ]

What is the point of doing that instead of the following?

[ "$VAR" != "value" ]

Does the 'x' have some special meaning?  (If so, are there any other
characters with special meanings?)

I have checked two books in my stash and neither of them mentions any
use of this syntax that I can see.