I may not have my car yet dammit, but I still have some questions

Mainly I'm wanting to know how helpful a cold air or short ram intake is, the pros and cons, and can you live without one?
I've been told things like a CAI makes your engine work too hard or that its pointless anyway since your car was built to take in cool outside air. I can clearly see that short rams aren't terribly expensive but wondering if they help as well.
Also perhaps what in your own opinion would be parts that are advertised to help but don't, underappreciated or overlooked upgrades, etc.