quote:It just depends on if you want there to be emphasis or not.
Emphasis, but also contrast. For instance:
A: Bhí tú ann? ("Were you there?")
B: Bhí. Agus tusa? ("I was. And you?")
A: Bhí mise ann, chomh maith. ("I was there as well.")
I wouldn't say the longer forms are particular "emphatic" here--
tú in the first sentence probably has about the same emphasis as
mise in the last. These forms just pop up when there's attention on the individual nature of actions or states.