Off road,
Bladestrike provides a good explanation. In the civil world companies decide how their pilots should dress. When this includes shoulder boards they decide who should wear how many stripes. Policies vary with company policy.
If you are flying by yourself you are in the fortunate position of deciding what you will wear. You have worked hard for your position and there is nothing wrong with wearing whatever you believe will give you the recognition you deserve.
But there is another reason. A uniform with appropriate insignia and shoulder boards identifies you as a pilot and can make routine airport tasks much easier. This is particularly true in those countries where a pilot uniform and appropriate ID are the only way you can access certain parts of the airport. Long ago I was turned away from the transient ramp at an airport in Asia because even though I possessed proper credentials, I was not in an acceptable uniform and therefore must have been off duty and not authorized to be there. I returned no more than an hour later in uniform with four bars and wings. I encountered no further problems.
Some helicopter pilots hate uniforms and consider it in poor taste to wear one. Damn the white shirts and forget the flight suits. They prefer jeans and t-shirts. These are often the helicopter pilots who complain they get no respect and moan that they are not paid equally with their plank driving brothers. You have to decide what you will wear-don't allow others to make the decision for you.