Thyroid does have a huge affect on your metabolism rate and thus your weight
. Too high and you can loose weight
, too low and you'll gain weight
Thyroid is also associated with mood including depression and anxiety. Some people can get off of or have no need to take anti-depressants or anti anxiety medicine simply by getting their Thyroid levels balanced correctly.
However there are other hormones in your body as well. They all have to be in proper balance and that can be tricky.