It’s important, certainly, but it’s not the only factor.
Whenever I hear people talking about going on a diet, the first thing I hear about is the exercises they plan on doing, whether its walking, weights, or whatever else. It’s kind of paradoxical, if you think about it, because the word “diet” implies something to do with food, yeah? But the stuff you eat always seems to be an afterthought compared to the workouts, and that’s not the right way to think about it.
The primary purpose of exercise is to build muscle and increase one’s stamina threshold. Burning off fat is just a side effect of the exercise process. You’ll certainly drop a bit of weight from a moderate amount of exercise, but if you work yourself half to death and then go eat a Big Mac, you’re not gonna get anywhere. The food you eat and the way you conduct yourself are much bigger contributors of weight loss, from proper nutrition to getting a good night’s sleep.
While we’re on the subject, if you’re only looking to loss weight in a single part of your body, then I’ve got some bad news for you: spot reductions don’t exist. You can perform all of the arm-centric exercises you want, but your body doesn’t prioritize any particular part when it comes to drawing on fat for energy. It just uses what it has, even if the location of what it has is nowhere near where the workout is going on.
If you’re exercising for the purpose of losing weight, then addition to the aforementioned nutrition and routine stuff, you should endeavor to keep your exercises and simple and concise as possible. You’re not looking to build up a bunch of gigantic muscles with complicated exercises, you just need to get your heart rate up and burn a few calories.