A dalton has two nice properties. One is that a hydrogen atom weighs one dalton, and a carbon atom twelve etc, so a mass in daltons immediately tells you rough

A dalton has two nice properties. One is that a hydrogen atom weighs one dalton, and a carbon atom twelve etc, so a mass in daltons immediately tells you roughly how big a molecule is in atomic terms. 100 Da is a small molecule, 1 kDa would be a peptide or macrolide or something, 10 kDa is a small protein, 100 kDa is a big protein, etc. The other is that a dalton is a gram per mole, so if you know the mass of a molecule in daltons, you can easily convert between mass and concentration at macroscopic scale. So, glucose is 180 Da, you can dissolve 180 g of it in 1 litre of water to make 1 molar solution. These properties are really the same property, because of how the mole is defined, but that property is useful in two quite different ways.