Most babies love baths. Sometimes if you have a cranky baby, just giving them a nice luke-warm bath will soothe them. You know how relaxing a bath can be for adults? Well, the same is true for babies. Think about it ... babies have been floating around in the womb for 9 months ... so having a bath is very natural for them.
Just never leave a baby, even a toddler, alone for even a moment while they are bathing, no matter how safe it might seem. Also, always make sure the water is only slightly warm. Hot water, even momentary, can be fatal to an infant.