Tank....Do we have to agression until the end?

Well since im wondering, i say why not ask....when fighting with a group of 6 or so ppl and doing raid bosses. Does tank have to do agression until the end or afer 1-2min of fighting you can just do once in a while?
or a person must have a SE to recharge him and continue until the end?

u have to hate then hit wuth ur weapon then when hates back use it again that all tank do at boss is just arest if u can stun and just spam hate thats all