For example:
It would be nice though.
vs.
It would be nice.
In a real conversation scene.
"It would be nice" is a neutral or positive statement, saying that if some thing were to happen, that would be good.
"It would be nice though" adds an element of wistfulness or regret. It is an acknowledgement that the good thing will not happen.
Off the top of my head I can't think of a conversation where I would say "It would be nice" on its own. Instead I would say "That would be nice" like so:
A: Would you like a massage?
B: That would be nice.
In that context "That would be nice" means "Yes, please."
A: Would you like a massage?
B: I don't have time. It would be nice though.
In that context "It would be nice though" is a polite way of saying "No." If it were to happen, it would be nice, but it will not happen.