In undergrad astro my long-term project was searching for eclipsing binary stars, which are paired stars that are aligned with us just right so that they eclipse each other as they orbit. We looked one by one at known variable stars that are easily found by taking a series of wide angle shots of the sky and watching for periodic variations in brightness. The reason we had to look at one star at a time was because we wanted to characterize the light spectrum as being either shifting (pulsing single star) or mostly constant.

It always blew me away that the reason we had a project like that to do was because not every star had been looked at.

This was before Kepler data came out and it will not really apply once LSST starts kicking ass.