Every time I put pants on with one leg at a time like the common person, I also put on a belt. Growing up as a ridiculously skinny boy, I have always worn a belt with pants because without it, I would have baggy pants and it keep it up with my butt. Like my friends, my belt is always there when I need it.
Being observant, I have realized that plenty of people do not wear belts with jeans and other pants. I feel odd not having my belt to secure my pants; does that make me insecure? I don't know how those people live without a belt. I mean, even Batman needs a belt!
Besides holding pants in the proper place, belts have more functionality. Belts are very fashionable, just look at all the belt buckles you can get!
And in my opinion, a belt can be a useful tool to keep healthy. Just think about it, everyday you probably put on a belt and tighten it to the same spot (notch) every time. And if you don't, you probably changed in weight (whether it's positive or negative is a whole different story). It's a great quick daily indicator on your health! So, there is no reasonable explanation for one (who wears a belt) to not notice weight change.
Remember that your belt should match your shoes! (Much easier if you have the same color belt)