Armor is used throughout the Dragonball Saga. The armor varies from light clothing, to flexible saiyan armor. Most armor in Dragonball is used for increased flexibility during battle. For example, while Goku was resting in the healing tank after the hard battle with Ginyu, Gohan and Gohan put on the saiyan armor. They said themself's that they feel very mobile and flexible in their new suit. So the armor really helps out in a heated battle. The durablitly of armor also helps. The Saiyan armor is very durable since it can expand to any size (This is why Saiyans can undergoe transforming into Oozaruu form without tearing it's suit.) Although it is very flexible, it can be penetrated. For example, when Vegeta was fighting Freeza's final form, Freeza knocked a few holes into Vegeta, therefore putting holes in his armor. The armor can also be used to train. For example, Goku used weighted clothing to train. This can help increase strength and speed.