Italian is a "pro-drop" language, which means that the pronoun can be dropped. It's not necessary for comprehension because the subject of the verb is evident from the conjugated verb, i.e. "I am" is io sono or simply sono.
Native speakers are far more likely to drop subject pronouns than to use them, except when the pronouns are useful or necessary in order to clarify, emphasize, make a contrast, or avoid ambiguity.