Does anyone still play Pokemon Go? If you are reading this, then probably you are still playing it the first few weeks or even days. At this point, if you are searching on how to manage your Pokemon inventory, checking out CP, IV, and other stuff, then probably you are a beginner.
Somehow, it is by everyone's preset - or maybe someone told you to do so, that when trying to free up slots in your Pokemon bag or inventory, you tend to dispose those that have the lowest CP. Say you have 10 Drowsy and decide to free up some space, you start transferring them from lowest CP then slowly work your way up until you feel that 'hey, this has a CP of 510, better keep it.' I bet you have done that at some point or even still doing it.
Stop trading lower CP Pokemon right away
If you read this part of the article, take time to double check before deciding to trade it off for candy, especially the ones with low CP. First thing you need to do is find out what the Individual Value or IV of a certain Pokemon is. To recap, IVs or Individual Values, are stats that aren't displayed as a readily read information Pokemon Go, you need to compute it in order to know.
The reason I'm telling you this is that it is possible for a lower CP Pokemon to beat the heck of an opponent of higher CP, if given enough power ups. For instance, you now have a couple of Ghastly and you need to get rid of one. One Ghastly has 10CP, the other has 120 CP. By checking out their IVs first, it is possible to realize that you need to keep the 10CP Pokemon and get rid of the one with higher CP. Why? Because the one with better IV can power up to a higher potential CP and also better IV gives better chances of winning during gym battles. CP works hand in hand with IV, and an explanation for this can be found here.
How to calculate IV?
There are third party apps or online tools that can connect to your account and automatically show each of your Pokemon's IV but I don't recommend using it as Niantic is pretty strict when it comes to terms and conditions, can't just risk being permanently banned because you are just trying to automate your IV calculation.
Anyway, there are 2 'legal' ways to get your Pokemon IV's. One is via various IV calculators that you can independently operate, it just needs some data input and you're done, one Pokemon at a time. This method requires manual calculation but is recommended because it does not risk you from being banned from Pokemon Go. One good IV calculator can be found here.
Another way is via the appraisal system, where you can just tap on the 'appraise' button on each Pokemon's stat view in Pokemon Go. This is what I currently use as I don't have to go anywhere to obtain the IV estimate. What I would do is everytime I catch a wild Pokemon or hatch an egg, I would right away appraise it. If I read good appraisal from my team leader, then I put a star on it, otherwise I just trade it off for candy right away. This method would save you time and slots on your inventory but not recommended when you are in a hurry trying to catch all the Pokemon that are spawning right around you.