People think that body kits are used for car only for the good looks but the truth is that they give more sophisticated good (sometimes bad) qualities! It's true that most of the body kits help to improve the looks (of course there are lot of awful looking body kits too....). In that matter, usual rule is that body kits improve the appearance of newer cars but not of the older ones. As an example, how if a body kit is fixed to a Austin A10 or something like that?
Now for our case lets think that at least we have a brand new "Suzuki Liana"! (Suzuki Liana owners don't get angry with me...) Just a joke! Lets get into the discussion again. So what are the other qualities added by body kits to our cars? Most important thing is that most body kits do improve the stability or the handling. That means improvement of degree of control-ability. Most bad quality added by a body kit is that the added weight. More weight implies lower acceleration, Less top speed and hard to control in corners at high speeds. But above things can be avoided by using materials like carbon fiber for the manufacture of body kits which are light weight. But since the carbon fiber is not affordable, most people use fiber glass which have much higher weight than carbon fiber. A well designed body kit will also have air intakes for brake disk, engine and intercooler (if you got one) to improve performances by cooling them down. So when you think about a body kit, consider above tips if you really want to improve the quality of your car... :)