Pronouns are not usually required As it can be determined from the verb endings who is performaing the action, the pronoun is not always required.
Como carne. (Yo is not necessary.)
I eat meat.
Comemos carne. (Nosotros is not necessary.)
We eat meat.
Comes carne. (Tú is not necessary.)
You eat meat
Pronouns used to avoid ambiguity. Certain verb endings, for example, come, could mean she eats, he eats or you eat, so we should add a pronoun to avoid the ambuiguity.
Subject pronouns used for emphasis.
Yo como carne pero ella no come nada carne I eat meat but she doesnt eat meat