The involvement of two types of molecular chaperone in folding newly synthesized proteins can be rationalized in terms of the crowded nature of the intracellular environment. Recent work sheds light on how these chaperones recognise their substrates and protect them from the problems of macromolecular crowding.
Ellis, R. J. (2004). Molecular chaperones: Avoiding the crowd. Current Biology, 7(9), R531–R533. https://doi.org/10.1016/s0960-9822(06)00273-9