Is there any difference between the usage of 'later' and 'later on'?
- I'll see you later.
- I'll finish it later on.
I would say the addition of the word “on” is more or less superfluous in almost every case. In other words, I believe later can always be substituted for later on, but not the other way around. When in doubt, later is the safe word to use.
Where you can’t use later on:
Later can be a way of saying goodbye, as a short form of “see you later”, but you can’t use “later on” in this way. Later and later on can both be thought of as short terms for “later on in time”.
As I see it, a hanging preposition. Occasionally "later on" may have a cadence that complements the rest of a sentence, but I see this as redundant language similar to "advocating for" rather than simply "advocating" (in most uses).
The Oxford English Dictionary just gives it as a synonym of the adverb "later", but to me there feels to be an expressive difference, at least sometimes. I think it has a connotation of including the hearer in whatever is going to happen. So in
or Later on.
the reply "Later on" seems less brusque, and more conciliatory. But it is a very subtle difference.