Why scientists care
Molecular geometry describes the three-dimensional arrangement of atoms. Electron-pair repulsions provide a remarkably useful first model for many main-group molecules.
Shape matters because it influences polarity, intermolecular interactions and ultimately many physical and chemical properties.
A concrete example
Water is bent rather than linear, so its bond dipoles do not cancel and the molecule is polar.
Try to notice
Science becomes memorable when a definition is connected to something measurable or observable.