The osmotic pressure method has the advantage over other methods as pressure measurement is around the room temperature and the molarity of the solution is used instead of molality. As compared to other colligative properties, its magnitude is large even for very dilute solutions. The technique of osmotic pressure for determination of molar mass of solutes is particularly useful for biomolecules as they are generally not stable at higher temperatures and polymers have poor solubility
This is the text from my Class 12 Chemistry Book Part 1 NCERT (India) (page 54). I didn't get why:
Molarity is used instead of molality. I think it is probably because we can measure the volumes of solutions easily using measuring cylinders, but mass of solvent in already prepared solution is difficult to measure.
It's magnitude is large even for dilute solutions. Why? I didn't get this one.