The addmob's SDK has its own inbuilt defence against ad spam. You can't with admob show adverts too often.
If you want to do that use mediation.
If you too often will ask for ads from admob and compliance coefficient will fall below 30% you will get frizz and ads will stop showing at all.
Admob doesn't always have a lot of ads for all countries.
If you want to do that use mediation.