As far as "need" .... first ask "What is it for (other than "Why, to sell, of course!")?
A rifle scope just allows you to see your target better. It is also easier for old eyes to focus on.....
For deer hunting, I'm with Art, you don't need anything bigger than a 3-9x .... and most of the time 3x is sufficient. A couple of the carbine length guns in the house have fixed 2.5x's on them- no sense in putting a large bulky scope on a deer gun that won't be used past 200 yards anyhow.... I keep mine on 3x, as there will be plenty of time to turn it up if the animal is so far out there that I need to see it better.....
For shooting smaller targets like prairied dogs at long ranges, something bigger would be better ..... but I shoot prairie dogs as practice for deer hunting, so I use the same rig (just lighter bullets, downloaded to similar speed as my deer load). 9x works.
For long range target shooting, or the very precise stuff like benchrest, ask somebody else..... I'm sure they have special needs which the rest of us do not.
As Art said, higher magnification makes close/moving targets more difficult- and in those cases, time is important. Diminished field of view can also lead to other problems- I missed the first buck I shot at when I was a kid- deer on the other side of a creek, maybe 30 yards....... but I killed the hell out of a 2" thick branch right in front of me.....
TheGolden Rule of Tool Use: "If you don't know what you are doing, DON'T."