I think that discussions that boil down to people just using the same word differently are obviously pointless if the word isn't the real question. I.e. debating 'is socialism bad' is pointless if both people can't agree on a definition of socialism. You end up with all sorts of 'no true Scotsman' type of arguments and the sooner everyone agrees on what they're arguing about, the better. But debates where the definition of the term is central to the very topic being discussed - 'is the EU a democracy?' - are fantastic ways to explore how we define these complex and abstract concepts - and often, it allows us to realize that we actually agree on a great deal but have different perspectives on the same fundamental reality.
"When I meet God, I am going to ask him two questions: Why relativity? And why turbulence? I really believe he will have an answer for the first." - Werner Heisenberg (maybe)