Maybe you could get away with it in a pub the size of my living room...but I generally find that in any situation where folks are drinking, some kind of amplification is required. And it's better to have a real PA than let individual instrumentalists use their own pieces according to whim...someone(s) will always be drowned out if they're not in that game.

Also, if you take a break, the staff puts the canned music on, it should be the same volume as the live music, more or less. And they amplify IT to suit themselves!

W-O