Looks like, in my non-native view, the usages of the word Up are pretty much always come with colloquial and informal tones. Such as...
Shut it! = Shut up!
Meet with = Meet up with
What's going on? = What's up?
Wait! = Wait up!
What on earth are you doing? = What are you up to?
Until this time where have you been? = Up until this time~
Am I correct? So if it is, is it simply a good advice not to use the Up at some writing tests or something?