I mean, really, as far as RAM goes... It's so cheap, it's circumstantial.
1) If you have 8gb now, and want to get more, you probably don't need it
2) If you are getting a new computer from the ground up, it certainly doesn't HURT to have 16gb. Maybe not help. It's so cheap, it doesn't even matter. What's another 8gb? $35?
3) You're a mac owner. 8gb can run you $200. Now you know why people make fun of you.