You have to send a sample of your soil to a lab and check which nutrient less in the soil. According to that you should add the fertiliser and note that we should add only fertiliser because fertiliser is nutrient specific.

nutrients enhances the crop to absorb the nutrients from the soil.It makes the crop to grow fast.

Disadvantage :
fertilizer causes water pollution. It can change the chemical composition of the soil.It will affect the aquatic animals in the nearby water bodies.