Expense: When it comes to the expense factor, watercolors score a good point as they are pretty affordable. If you are just getting started then this factor will definitely push you to pick watercolor as your medium.
Large area painting: Another advantage you have with watercolors that they are pretty easy to use when you want to cover a larger part of the painting with colors. So if you are adding elements like water or the sky in your painting then using watercolors will definitely provide you with an advantage.
Dilution: You will see that while painting, you will often need to dilute the paint to get the right shade. With watercolors dilution or even making the paint easier to use is fairly simple.