So what it's confirmed by now it's that
1. Sakura's forehead thingie is a seal and it's not the Yin one.
2. She needed 3 years to gather all the chakra.
3. It boosted her stamina, strength and speed.
As we all presume, the seal is here to stay. And I will try to clarify why, later on.
Hmm? I don't agree with the bolded.
My opinion on this matter.
The appearance of the seal only indicated that she has reserved enough chakra so that she can release it any time. Meaning that she doesn't have to reserve chakra anymore and can use her base ability 100%.
I will explain this using dragon ball LOL.
Remember Goku training in a heavy gravity environment called "Kaiousei"?
Because the gravity is so heavy, he's severely handicapped and his moves are less powerful, his speed are more slow.
THIS is what Sakura has been going through all these 3 years. Basically she had to reserve her chakra so she can't use her full capacity. Therefore slowing her speed, and lessening her attack powers.
Now, remember how Goku returned on earth?
His speed and power has increased tenfold because there is nothing holding him down. Earth has basically no gravity compared with Kaisousei.
THIS is what happened to Sakura when her seal has appeared. She doesn't need to reserve her chakra anymore. Therefore nothing is holding her down. She can use her capacity 100%.
The point is Sakura hasn't turned Super-Saiyan(released her seal) yet, therefore it hasn't boosted her speed and stamina. The speed and stamina looked like it was boosted only because her previous situation was handicapped.
This is my take on the matter. And I agree with what the Japanese forums are saying that she was only fighting with a part of her chakra reserves for three years.
Edited by ramenanmitsu, 30 May 2013 - 03:44 PM.