Oil is 4% wth a 4k cap, so once you're over 100k oil, don't keep the excess in the CP.
I usually collect loot from the command post after each war for the following reasons:
Having said all this, I know of many allies who keep the loot in the CP. To each his/her own.
- There are many reports of missing loot from CP
- I might forget to collect the loot before it overflows from the CP
- I like knowing how much resources I have and having it all in one place
- I don't need to protect my CP