Strictly speaking, when a Hathan (bridegroom) gets married, he should recite the blessings himself. If he gets married through a Shaliyah (agent) then the agent recites the blessings on his behalf.
Nowadays, as we know, it is customary for the Meqaddesh (one performing the ceremony) to recite the blessings, so that the Hathan would not be embarrassed if he did not know them. Therefore, since the one reciting the blessings is doing so on behalf of the Hathan, it is essential that when he recites them he has the Hathan in mind. The Hathan must also concentrate on the blessings and intend to fulfil his obligation through them. It is also appropriate for the Kallah (bride) to concentrate on the blessings and for the one performing the wedding to have her in mind too.
If the Hathan did not pay attention to the blessings, there are some who say that it does not matter. However, since there are those, including the Rambam, who say that in such a case it would be a blessing recited in vain (Berakha Lebatalla), we must be concerned, initially, about their opinion.
(See Ben Ish Hai, 1st year, Parashath Shoftim, Oth Beh)
