The first- and second-person verbs do not need a subject pronoun because the ending of the verb is sufficient to identify the person in most of the conjugated forms of a verb.
Adding a subject pronoun where it isn't required for clarity (like in the third person) is just adding emphasis.
hablo = I speak, I'm speaking
yo hablo =
I speak,
I'm speaking
If emphasis isn't your intent, don't use the
superfluous subject pronoun.
