Inter-individual differences can inform treatment procedures and - if accounted for - can improve patient outcomes. However, when studying brain anatomy, these variations are largely unaccounted for. Brain connections are essential to mediate brain functional organization and, when severed, cause functional impairments. Here we reviewed the wealth of studies that associate functions and clinical symptoms with connections using tractography. Our results indicate that tractography is a sensitive method in healthy and clinical conditions to identify variability and its functional correlates. While our review identified some methodological caveats, it also suggests that tract-function correlations might be a promising biomarker for precision medicine.