It is a difference between English and Japanese.... usually if the speaker is referring to themselves, the noun (their name) is left out completely as implied. Naming oneself is for
a) if its unclear who is the subject without it.
b) its also considered "cute" if used excessively by young women.
Iku! (not necessarily clear if the user means
I go, you go, or
we go).
Ami iku! (its now clear who goes).
Watashi/atashi/watakashi/boku/ore are actually used pretty rarely in casual speech (many of the formal verb endings are dropped as well) - and these are trendy teens so the rough, casual level of speech is even coarser.
Spoiler for example in ep 17, an important plot revelation about Kitamura that involves how he refers to himself:
I thought it was interesting to watch Kitamura consciously switch from the formal neutral "watashi" to the more masculine assertive "ore" when confessing to Sumire. To some extent he was trying to sound as rough as she does
.