I happened to hear one of my colleagues leave a voicemail message along the lines of:
"Hey, it's just [name] in relation to... blah blah blah."
Then it happened again... and again for a third time.
Can you see what I'm getting at here?
When you say, "hey, it's just me," you're trying to come across as easygoing or unthreatening, and perhaps you're trying to make the other person feel like you're going to help them out.
Unfortunately, the casualness that you're trying to portray can work against you.
To put it simply: it removes whatever power you had before engaging in the conversation. You might even be saying, "you don't have to take me seriously," albeit subconsciously.
Why shouldn't you be on the same level of whoever you're talking to? That goes for your boss or some random person on the street.
This whole 'just' thing is relevant when you're talking about yourself.
I meet doctors all the time and I sometimes fall into the trap of saying, "I'm just a writer."
Sure, a doctor has way more years of study under their belt and they have a very hard job (understatement) but there's no reason why I should feel like I'm not good enough. There's no reason why you should feel like you're not good enough.
We are all people and we should be treating each other as equals. If you say 'just' a lot, try your best to drop it and you might find yourself gaining more power in conversation.
Some basic psychology knowledge helps when you're writing. See some of my work here. Find out more about me freelancing for you here.