#1 Impressions aren’t everything but they do matter and can send a message that cannot be as easily and quickly retracted as it was conveyed.
#2 Normally, it is advisable to look impeccable, neat and tidy, collected and well put together, but this doesn’t apply to all situations. For different reasons, you may instead wish to portray another persona, a certain state or condition, or what they may be or have been through.
#3 Dressing for the occasion isn’t a meaningless arbitrary requirement to always dismiss. It shows consideration & respect for a given event and denotes participation and belonging. But whether you can or will do that, and to what extent, is for you to discern and decide.
#4 Stressing about being overdressed or underdressed in comparison to others is mishandled energy. As long as you keep it between acceptable parameters, it will be fine (unless it is for something particularly strict).
#5 Having your own personal style can help you stand out and preserve your individuality. It also introduces you to others without words. It doesn’t necessarily mean that those that don’t, do not honor their own traits and preferences, but when you do, it becomes evident.