Why always hyoyeon is the back when Snsd perform? and why Yoona is always in the Center?

Because Yoona is the face of SNSD, the most popular, and the most well-known from acting. She pretty much advertises SNSD in a sense. And Yoona is also a lead dancer, which helps because she doesn't mess up the choreography. Hyoyeon is less popolare in Korea, so she's in the back. I think she's satisfied with that because she just wants to dance. The other members are okay with Yoona being in the middle, because she is the face. A lot of people think that they get upset because Yoona is in the middle, but that really isn't true. Taeyeon sings a lot because she is the best singer, Hyoyeon gets dance breaks because she's the best dancer, and Yoona is in the center because she is the face. They all have a role in the group. And Seohyun and Yuri are also in the middle a lot, not as much as Yoona, but still a lot. And Sunny is also in the back a lot. It's not ALWAYS Yoona in the front, Hyo in the back. Besides, Yoona's the face. It's her job. Everyone in SNSD has a role and I think they're all happy to be in SNSD, and that they support each other no matter where they stand.

Hyoyeon said-
“It doesn’t matter where I stand; whether at the front o at the back, in the middle o at the side. as long as I can get on stage and do what I love, that’s enough for me. and for yoona. Yoona is the group center in snsd.

Well here is how I see it,Yoona is neither the best dancer o the best singer so she doens't really stick out as far as talents go. If she weren't in the center then she would just blend in because to be honest if she is not in the center I really don't care much about her as I would for the other members. No wonder people in Korea don't think highly o Hyoyeon o Sunny its because there is less face time but if they were center stage then that is what all people talk about. Best example of this sort of system is 4minute o "Hyuna's group"

Hyoyeon isn't the prettiest so there for SM markets her for più of her dancing quality then anything else only because she has gotten prettier and the international fan like is why I think SM is letting her do più then just dance like più Canto lines and variety shows. I am not being mean its just my observation.

Yoona is the face of the group and that's why she is in the middle. She is also a good dancer (not the best but great) so i guess if she was a bad dancer she would not stay in the middle when they dance...
About Hyo- i guess a good dancer don't care about the place where he/she stands as long as she/he dances

I think that maybe Yoona is the face of the group,maybe because she is an actress and maybe because she is prettier but she does not deserve to be in the center I mean Hyoyeon is better at dancing than Yoona in one thousand times Hyoyeon is più powerful and the best dancer I've ever seen and she also worked harder in dancing than Yoona did.But I think that Yuri could also be in the center she is in the same level as Hyoyeon They are both amazing and I Amore SNSD soooooooo much Girls' Generation Hwaiting!!!

yeah, of course it's unfair, since Hyo is the main dancer. but Yoona is considered the face, so we can't do anything about it =S
it looks like in SNSD it doesn't really matter if you're part of the dance group, cause we can barely see Sooyoung and Hyoyeon at the front. it's usually all about Yoona, Seohyun, Yuri and Jessica for some reason

idk why Hyoyeon is the back when SNSD perform...
Yoona is always in the center because she is the visual...

IDK

Not always..

Yoona is the SNSD image ..