Alright. Let's say you have two choices in front of you: 1) reduce weight or 2) increase horsepower. Which do you do? Well, the obvious answer is both. Of course. For the sake of this discussion, though, let's assume we focus on one or the other initially. In that case, the answer should maybe be weight. Here's why: as a general statement (that I will certainly stand behind), car performance gets better as you decrease weight. By "car performance" I mean pretty much every possible performance topic. MPG, acceleration, corning/handling, turn-in, braking. Everything. At the end of the day, thy true foe is weight. Shed Those Pounds There's another benefit to decreased weight, and that is reliability. When things are heavier, components end up being stressed much more than they would be otherwise. Lightening the load on those components has a net result of increasing the lifespan/reliability of those components. This applies to most aspects of car activities: drag racing? Lose the weight. Road racing? Lose the weight. Rock crawling? Yes, lose the weight. The Intangibles Something else, as a result of lightening the load, is the feel of the car. It can be considered intangible and subjective (after all, "feel" is something that is different from driver to driver), however lighter cars will tend to feel more nimble, more eager. More like the car is reading your mind. Heavier cars will feel more "boaty" and perhaps like they are fighting you. A lighter car will feel more balanced, more fun to drive. It isn't something that can necessarily be mathematically calculated, but contributes to an overall feel of a car. More times that not, a sporty lighter car that has been setup properly will feel loads better than a sporty heavier car that has been setup properly. But It's Sooooo Hard And here's the rub. Unfortunately, it's not really easy to lose weight on a car. Especially if you care about things like, oh I don't know, comfort. Like A/C. And sound deadening. That kind of stuff. The typical way cars shed a lot of weight is if/when they become dedicated track cars. This is at the sacrifice of comfort. This results in most enthusiasts just adding power. That tends to be easier. And ultimately, it's what you want to do anyway. But think of it this way - each time you add power, if you could also lighten weight somehow, you will be adding power on steroids. So if you have the money to spend and inclination (and don't have to worry about legality in certain racing classes), before you just through a bunch of power at a car - think about what you can do regarding weight first. Fiberglass/CF hood and trunk? Fenders? There are things you might be able to find that can be removed/replaced with lighter components without sacrificing comfort, especially if you DD the car. And of course, every car is different in what can be done.