1 - If you have a lot of peripheral stuff (scanner, external HD, printer, webcam, etc.) each device you plug into your USB will draw a tiny bit of energy, but it asdds up and can choke your system. When we buy a new computer, one of the immediate things we do (because we DO have a LOT of peripherals) ir slap in a 900Ws power supply ASAP.

 

or you can use externally powered USB hubs. (which is a good idea anyway)

Airport security is a burden we must all shoulder. Do your part, and please grope yourself in advance.