The total stellar mass of a galaxy cannot be measured directly. Astronomers can infer it from the galaxy spectrum by stellar population synthesis. However, since high-mass stars dominate the spectrum but contribute little to the total stellar mass, the inferred total stellar mass is sensitive to initial mass function (IMF) which is usually assumed a priori. One can also measure the total stellar mass by kinematics, but it is the total mass of stars, dark matter and gas enclosed that is measured in this way, and we still need some assumptions (say, on the dark matter profile) to obtain the total STELLAR mass. In a word, it's very difficult to measure the total stellar mass of a galaxy precisely.
So I wonder why people are still interested in this parameter. What can it tell us about the formation and evolution of galaxies?
It seems that what can be measured relatively more accurately is the properties of high-mass stars which are also the main sources of stellar feedback and metal enrichment. Why not just focus on these stars? What makes low-mass stars (or to be more concrete, their mass) important to the galaxy as a whole?