The only job a wedding guest should have is enjoying themselves.
There is no question about it: planning and setting up the average wedding is darn hard work. While it is meant to be a special day for both the bride and groom to look back on fondly for the rest of their lives, the stress of making everything perfect can overwhelm the happiness they feel about tying the knot.
While the bridal party, groomsmen, family members, and wedding planners are supposed to help with much of the craziness, that can still leave a couple feeling like they have a lot to do. It is only natural to want as much support as they can muster from willing helpers who are also invested in making the day go well.
However, there is a difference between a close person to the bride or groom actively volunteering their services and insisting that somebody has to put the work in without their knowledge. With all the thought and logistics that go into weddings, everybody involved must give enthusiastic prior approval that they want to do their bit. If that doesn’t happen, it is a recipe for resentment and things potentially going wrong.