Is CP even a useful stat anymore?
I know it is a reflection of the other core stats (hp, att, def, lvl). And the core stats will always be useful, but CP is not a core stat; it is just derived from the others. So now that gym level rankings are no longer based on CP, what use is it?
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Mabe personally ranking your same pokemon/same moveset in your inventory i.e. (which is your strongest vaporeon with hydropump). But this is a limmited use. Type advantages seem to dwarf the importance of CP rankings between different pokemon now.
Answers
Well, until they make even bigger changes, it is a general indication on level and IVs of the Pokemon.
The game doesn't actual tell you the level and IVs, so you have to guess based largely on CP.
IVs - if you hatch a pokemon, you have an idea of IVs by the CP.
Level - you have a very good idea of the level of a wild caught Pokemon by the CP
