The negate a gaffe rule is in there for two distinct reasons. The first has to do with differing play styles when it comes to social interactions. Some GMs prefer the let the dice to do the talking. Other GMs expect their players to do the requisite chatting. The latter sort of forces players to roleplay, but the reality is that not all players possess the social skills their characters are supposed to. Personally I prefer the middle ground -- if players want to chat it up, great, I may modify the roll based on how they do. But I'm also fine with doing rolls. I don't believe in penalizing players for being introverts or less social, though. So if someone does try, but they aren't as suave as their character should be, I think they should have a chance to fix that in case they mess up. The second reason is because EP is a complex setting. There's a lot for new players to absorb. A player less familiar with the setting is more likely to make a social gaffe than someone more familiar. So in that sense, it's a guiding tool, in the same way that GMs can call for Know skills tests to fill players in on things their PCs would know about the setting. Same goes for Insight for clues and Flex for narrative control -- we are not all secret agents and won't always be able to anticipate things we might need on a mission that our trained PCs probably would have thought of.