Stars form inside the densest parts of giant molecular clouds (GMCs) and its rate is tightly linked to the amount of dense molecular gas suggesting a universal star formation process. However, extragalactic studies of nearby galaxies show that star formation does not occur universally across and within galaxies, but depends on the structural and dynamical environment in which the GMCs reside. In my talk, I present recent surveys of dense molecular line tracers inside the MW (LEGO, IRAM 30m) and in nearby galaxies (ALMOND, ALMA) which aim at gaining a deeper understanding on the efficiency at which the dense gas phase is converted into stars. I will show that both the star formation efficiency and the fraction of dense gas depend on the properties of giant molecular clouds and that these can couple to the ISM environment. Moreover, I will discuss how these results connect to the more constant star formation efficiency observed in the Solar Neighbourhood.