What's a mind game and is it a good thing?

What is a mind game? Is it bad or good?

Mind games are bad
This is used by someone who tell's you one thing then changes the words around and it sounds like something else. Sometimes people say things to a person and knowing that is what the person really wants to hear. An example is if you ask someone if what your were looks nice they will tell you exactly what you really want to hear. These are just a few examples I can think of.

Same as 'manipulation': to control or play upon by artful, unfair, or insidious means especially to one's own advantage....to change by artful or unfair means so as to serve one's purpose.