U.S. Department of Energy, around 90% of the energy costs in doing laundry in your washing machine comes from heating up the water, and twice as much is used for hot water as is for warm.
So, you save a lot of energy (and therefore, help your monthly budget) by washing your clothes in cold water.
But will they get clean? Sure. If you've got some stains with oil in them, they may need some special treatment (rub your laundry soap into them directly before putting the item in the washer). And, you'll be wise to use those cold-water detergents that are made for cold water laundry.