The subject of a verb can be seen
from its conjugation, therefore it's not necessary to keep the pronoun unless you wish to
In fact, you should only keep the nominative pronoun in a sentence to emphasise something,
and it's wrong to keep it otherwise.
- hogy vagy? how are you?
- te hogy vagy? and how are you?
- itt van a barátnője here is his girlfriend
- itt van az ő
barátnője here is his girlfriend
- ott van a barátom there is my friend
- ott van az én barátom, hol van a tied? there is my friend, where is yours?