Hello Anton. But here you are referring to the first personal pronoun "I " only ,what about the others , when you want to say , he ,she ,we ,,, you can't just write " gotta go " , or "see" and anyone will know you refer to "we" or "They" ,so even in colloquial English you will have to use the personal pronouns to indicate who you refer to .Obviously only in the case of the 1st pronoun "I" and only in colloquial English as Patty mentioned could you omit the pronoun . So the pronouns are of a significant importance in making the sentence comprehensible .

yes..you are right..only use these phrases in colloquial english..NEVER do that in an essay unless you are writing a dialogue and it has to be authentic...

We use "See.", when we want someone to see the point that they are trying to make, it usually means (I told you so, so look!". "I see" is the same as "ponyatno" po-russkii. (Means the same as I understand your point, or suggestion. Using "Mean smth. ..." is colloquial, using "I mean smth", is more accurate, use that when you have made a mistake in what you just said/wrote. "Gotta go." is colloquial for "I have got to go", also "I gotta go."is also colloquial because it misses and ignores all rules of grammar. Join my group about English, I can explain more there :)