Dandelions will push out grass and other plants as well as sapping water and nutrients from other plants.
You can get rid of dandelions by being through and patient. There are several ways to control Dandelion. All methods to remove Dandelions must be performed every year because their seeds can travel very far on the wind.
You can either use an herbicide or hand dig which can be time consuming and should be done in Spring when the seedlings appear, but you must ensure you have pulled the entire tap root.