Giving every sim a formal outfit is like a guilty pleasure of mine. Sometimes I even go out of my way to make them look especially elegant and beautiful, but it's a complete waste of time because I never use those outfits in gameplay. If we ever get lot traits that allow us to set dress codes, that might change, but as it is now, aren't weddings pretty much the only occasion for sims to show up in formal attire? I've had maybe three weddings since I started playing the game in 2017, so... yeah. Completely useless, yet I keep doing it. :D
In my defence, though, it's never more than one in the formal category. That's also true for the more sophisticated of my sims who always dress rather formally, because in their case, they're wearing suits and dresses as their everyday outfits, too.