The most important thing, in my opinion, is mental baggage. This is the amount of your attention that is taken up with an extra bag & all that extra stuff. There is a mental weight associated with all that stuff. Less stuff not only makes you physically lighter & faster but mentally (& arguably emotionally) lighter & faster as well.
You’re not thinking about what thing goes in which bag. You’re not worrying about the cost of checking that bag. You’re not worrying about them losing your bag. When you’re carrying everything with you, on you, you don’t have to worry about anything. You just go: you are awesome.