Cara Pils is just a tool. Often times it is not needed in a recipe. For instance, a lot of IPA recipes have a lb of crystal and then a lb of cara pils - in that case it may not be needed. But if you are trying to increase the mouthfeel of a beer and for whatever reason and don't want to mash higher it can work. I also think that in the case of lighter lagers you can taste the cara pils. In an IPA, not so much.