What you wear affects how fast you move. The heavier the clothes/armor, the slower you run. For example, wearing the Enclave Power Armor gives you good damage resistance but you move slower because it weighs more. Wearing a Lab Technician Outfit on the other hand, gives you very little protection but you have more mobility. It's a good idea to find a balance between speed and protection to help increase your chances during your travels through the wastelands.