If the wedding is large, you may need two sets of dresses, one for pre-wedding activities, such as welcoming guests and taking photos, and the other for formal wedding ceremony. But this situation is not necessary, mainly depends on the personal preferences and budget of the bride and groom.
It is suggested that when choosing bridesmaid dresses, we should fully communicate with bridesmaids, understand their preferences and body characteristics, and try our best to choose dresses suitable for them so that they can show their best state at the wedding.