Except for the problem of propagation losses
You'd not only have to convert 100% of the matter to energy, you'd have to transmit it over a distance without any loss and then reconvert the energy back into the original matter. Remember, e=mc^2 works both ways. If you lose energy during transmission, you'll end up with less matter at the other end. That wouldn't be a big deal if the lost matter were useless fat but it'd be a bummer if it were brain tissue.