If you look great in said dress and really, really want to wear it to the wedding, go for it. Maxi dresses are generally best for more informal and or summer weddings, since wearing such a dress to a highly-formal winter wedding is just going to look….strange. Avoid white maxi dresses for obvious reasons, and keep in mind you’re going to end up in a least a few photos, so you want to look as stunning as possible. You certainly don’t want to wear something you’ll cringe about for the next how-many years.
Should you still be unsure whether a maxi dress is appropriate, feel free to ask the bride if she’s a close friend, or a member of the bridal party. You can also look at the wedding website to get a feel for the theme, if applicable.
Again, if you feel confident and attractive in the maxi dress and it won’t look out of place at the wedding, rock that thang and have fun!