It is not incorrect, its the same but we tend to avoid the pronoun since the conjugated verb already tells you who the pronoun is, particularly if you're talking about yourserf . we say YO in cases that enphasis is needed when talking about yourserf , if you say YO many times you might sound egocentric. Hope this helps :) Saludos

Está es una explicación con ejemplos. Yo soy..........................................Yo estudio Usted es.......................................Usted estudia El es..............................................el estudia Ella es...........................................ella estudia Nosotros somos..........................nosotros estudiamos Ustedes son.................................ustedes estudian Ellos son.......................................ellos estudian Cuando usamos " soy " sólo hay una posibilidad.....................estudio Cuando usamos " es " hay tres posibilidades..........................estudia Cuando usamos " somos " hay una posibilidad.........................estudiamos Cuando usamos " son " hay dos posibilidades.........................estudian Más de una posibilidad da lugar a confusión. In english I am ..................................I study You are. ............................you study He is. ................................he studies She is.................................she studies It is. ...................................it studies We are................................we study They are. ............................they study You are................................they study I was................................Yo estaba....................... yo estudie You were..........................usted estaba..................usted estudio He was.............................el estaba.........................el estudio She was............................ella estaba......................ella estudio It was.................................esto estaba.................... You were. ..........................ustedes estaban.........ustedes estudiaron They were...........................ellos estaban..................ellos estudiaron We were.............................nosotros estábamos. .......nosotros estudiamos Cuando hay una y solo una posibilidad no da lugar a confusión. (Nosotros) estábamos (Yo) estudie (Nosotros) estudiamos

"Soy" and "yo soy" have the same meaning, but when you use only "Soy" you are using a tacit subject, so everybody will understand "yo soy".

It's not incorrect but we don't use personal pronouns when we talk about ourselves.

No! Both are correct. "Yo soy" is just more complete and eliminates doubts about the subject, if the person who you're talking to didn't know that "soy" refers automatically to "yo".