On the Reddit I read the following comment from SN811 "The PoW concept in relation to digital cash was introduced to solve a certain problem at a certain time (it's really an extension of hashcash in that sense). Anyone who designs a system based on PoW in 2014 does not understand really the purpose in the first place."

Can somebody please elaborate on what he is talking about or at least point me in the right direction?  What exactly was the "certain problem at a certain time" that is being referred to?  It seems vague to me.