They allow each friend to dress for her personal skin color and body type.
If there is one thing every women knows, it's what silhouette looks best for her body type. By not forcing your friends into one style dress, you are giving them the opportunity to feel their best on your big day. If you are going with the same style dress, but allowing a broad range of colors, this will help women with different skin tones find the most flattering shade.
For some wedding themes, such as vintage or boho, mixing and matching is already a part of the decor.
Above, this boho wedding employed mismatched dresses to extend their decor style through to their bridal party look. The result was a laidback, but very stylish, vibe. Although you could certainly find one dress to fit the theme of your wedding, some themes are highlighted with a mix and match aesthetic.
By not selecting one dress for everyone, you allow each bridesmaid to shop within her own budget.
Why is it that the dress you really want is always the most expensive? By asking each friend to select her own dress, they will do their own legwork to find an affordable option, if that is a priority for them.
Unless you are really communicative about color and style, your bridal party might look too mismatched.
Mismatched can sometimes look messy. Especially if you aren't clear in your expectations, every friend will translate your requests differently. For example, you might be thinking about blush when you say "light pink," but then you might end up with three bridesmaids in a bubblegum hue.
Having every bridesmaid wear the same dress can present a cohesive appearance, especially for a really large bridal party.
When you've got a bridal party in the double digits, that's a whole lot of people up at the altar. Not only is it a simpler route logistically (12 women all trying to create a well-done mismatched look? Total. Nightmare.), it also will make it easier for the guests to focus on you and the groom rather than the variety of dresses in front of them.