Epaulettes generally seem to be scorned in the helo world as being pretentious. They are. However, I do believe they should be worn when flying pax because they like to think they have a professional pilot behind the controls and wearing epaulettes fosters that image. They feel happier, and the happier they are, the better tips you will get. In theory anyway.
They are also very useful when flying in places like Africa when you have to deal with petty officialdom with an overinflated attitude and a desire to fill their pockets. Some are still slightly impressed by anyone wearing visible rank and they will sometimes even accord a little respect. You can get away with more and I have marched through restricted areas, to find the above officials on their extended lunchbreaks, with a confident attitude and a "take no c**p look", and people are more hesitant to stop me. Wonderful! I have not used them much otherwise. It helps if a company has guidelines and tell you when to wear them. Most guys/gals wont wear them because they think they will look like an idiot. If the company says they must, then they can prance around with bars and feel important without feeling guilty.
There is nothing wrong with wearing bars, you have worked hard for them and you should be proud to wear them, just choose where and when you wear them. Do not wear more than you are entitled to and it looks stupid if you wear them around town.
The original question has been answered but it did not cover WHEN to wear bars.