Difference between a subsub domain and subdomain/child domain?

What would the advantages / disadvantages be of these two different setups in a active directory environment? Apologies for my lack of correct terminology please correct me as to the name of subsubdomain..

Root of domain tree :domain chicken . com
Subdomian internal. Chicken. Com
Sububdomian external. Internal. Chicken. Com

Second scenario :

Root of domain tree: chicken.
Subdomain : internal. Chicken. Com
Subdomain : external. Chicken. Com

I hope I have explained this okay, would be grateful for what the differences would be and advantages /disadvantages are?

Many thanks