Strong lensing of distant galaxies by other galaxies or their clusters can reveal supernovae outbursts in high redshift, otherwise invisible. Gaia will be possible able to detect these as new sources located in vicinity of a gravitational lens. It will probably be limited only to the closest lensed galaxies.
from Sullivan et al. 2000
Example application of lensed SNe: modelling the dark matter haloes of lensing galaxies (Jonsson et al. 2010.