High-angular resolution observations using interferometry allow fundamental measurements of properties of stars, which are crucial to test stellar models or empirical relations. For example, the combination of an angular diameter with a measured parallax (distance), a linear radius can be measured with little model dependence. Angular diameters are also needed to calculate stellar effective temperatures. A review article highlighting the power of interferometry (in particular when combined with asteroseismology) can be found here.
The Center for High Angular Resolution Astronomy (CHARA) at Mt. Wilson observatory hosts an interferometric array consisting of six 1-m telescopes, with baselines ranging from 30 to 330 meters. I am a science team member of the optical PAVO beam combiner, which was built by Mike Ireland and is one the highest angular resolution astronomical instruments worldwide (allowing diameter measurements down to ~0.3 milliarcseconds, ~5 million times smaller than the angular size of the Moon).
Together with Tim White I am the co-PI of the first dedicated CHARA campaign to measure angular diameters of asteroseismic stars. The plot on the right (from Huber et al. 2012) compares interferometric and asteroseismic radii for a sample of Kepler stars (black) and bright stars with asteroseismic detections from ground-based campaigns (red), proving that asteroseismic radii are accurate to ~4% for dwarf stars. Asteroseismic densities can be combined with interferometric radii to measure masses of single field stars with little model dependence. I have also led a study to use interferometry to validate the detection of an exoplanet. We are currently working in expanding the sample of stars with asteroseismic and interferometric measurements (in particular for red giant stars which are valuable for galactic archeology).