Traditional Irish Music
I have not used an amplifier at sessions myself, but a friend of mine has. I should explain, however. His piano does not have a built in power amplifier or speakers. Without the external amplifier he would be voiceless. My piano does have a built in "power" amplifier and speakers, but in all but the smallest sessions it is not loud enough. I have resisted carrying an amplifier as an electronic piano player is already (as you know) burdened with carrying the piano, a stand, extension cords and perhaps a throne or chair. I have to use a two wheel truck to haul everything. An amplifier is obviously yet something else to carry.
Now, our sessions here in the states are held in rooms far bigger than anything I have seen in videos of sessions in Ireland. No one would lift an eyebrow at an amplifier for a keyboard. A guitar player with an amplifier would probably get lynched.
I have been playing piano more or less irregularly at the local Irish Sessions since 1995. I prefer to use a Roland Digital Piano with built-in speakers because I do not need to bring my Peavey KB-100 Amp with me to the session. Besides the Digital Piano, I bring a stand for it and a bag with the necessary chords. Also, my Digital Piano (which I refer to jokingly as a genuine imitation piano) does make a halfway decent imitation of a real piano sound.