what does kamae mean?
Kamae means, posture, pose, style or stance.
The verb Kamaeru means to prepare in advance, to plan or to scheme. Which means that Kamae is an intention that is taken deliberately.
Kamae gives you an advantage.
Also, you can make the opponent think that he is at an advantage, while it's actually his disadvantage, by provoking him to act as you want him to. Hence, Kamae can be called an intention.
Here's details of Hanmi Gamae
To take such a stance, you should tense some muscles, else your body will collapse. We call this necessary amount of tension natural tension, passive muscle, or in this case:
Required Energy. It prevents the body from dropping 
"ps": neko no myojutsu
It can be understood from the story “Neko No Myojutsu*” eventually you should move without intention.
Kamae should actually exist without hesitation or conscious thought for that matter. Intention can be a source of power, but intention can be read as well putting you at a disadvantage. However, it is very difficult to try to move without intention. It is simple, if you think “without intention” you are already intending.
Practice with intention until movement comes out naturally in Jiyu Kumite.
*PDF Download I found the file online years ago. It's not my work.