A.
1. dia baik, cantik, ramah.
2. dia itu...baik, cantik, ramah.
The situation: when someone is talking about someone else (function: to give an opinion, to describe). Before giving out opinions or describing, the speaker might firstly "think" of the words to be given to somebody else, then the word "itu" is given there after the subject. In english, I think it's same like "she is yeah.. kindhearted, pretty, easygoing". As you know, it sounds more natural in conversation. But remember, to use it only for daily conversation and casual writting.
You can replace "dia" with other personal pronouns, e.g. "aku", "saya", "kamu", "anda", "mereka", "kami", "kita", "(a person name)" etc.
Another example.
1. Saya belajar memasak sejak SMA.
-I learned cooking when I was in high school
2. Saya itu belajar memasak sejak SMA.
-I learned cooking when I was in high school
From the examples above, there is no certain situation to use the word "itu" after personal pronouns, but, just to sound more natural in conversation (and no specific function, tbh. Well, if you see, even the english translation has no difference at all).
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B.
Remember, the word "itu" has a different meaning if you use it as a demonstrative pronoun.
For example:
1. Mobil mahal.
(the expensive car)
2. Mobil itu mahal.
(that/the car is expensive)
Note: The first, it automatically becomes a noun (formula: noun + adjective = noun), without the word "itu". The second, with the word "itu" is pointing out a specific noun, or as a demonstrative pronoun (another example: "mobil ini mahal" / this car is expensive).