A lot of couples do first looks these days, and to some it seems like its just a trendy thing to do, when in fact there are a lot of reasons people do it! There are many positives and a couple negatives for doing a first look, its not just about doing something because others are doing it, see below for my input.
It saves time.
I'm a pretty fast shooter when it comes to portraits, and I must say I still get a little stressed about time when couples don't want to do a first look. Wedding days pack so many things into a short period of time, so if you want to be present for more of your wedding, or want a lot of photos, a first look is your best option. Couples often do a first look, and then portraits with their wedding party and/or immediate family before the ceremony to get those photos out of the way. If you have a large family and need a lot of different combinations of family photos, it would be beneficial to do immediate family photos before the ceremony to get them out of the way. If you don't do a first look and have a lot of portraits you want done, I would recommend having an extended cocktail hour, around 1.5 hours instead.
You can go to other locations.
If there is a nearby spot such as a gorgeous park or forest, it would be unrealistic to get there during cocktail hour if you have family photos to do. If you do first look and take care of some of those portraits beforehand, you have the option to hop in the car and visit another spot.
Your hair and makeup will be fresh.
You'll get portraits before you do any ugly crying, or have too many glasses of champagne! Definitely a plus for your looks! If you don't do a first look, a quick reapply of lipgloss and some powder after the ceremony is the next best thing.
It's more private.
If either of you is nervous about being the center of attention at your wedding, you may like to have the first time you see each other just the two of you and not in front of all of your wedding guests. This way you can be yourself, hug, kiss, laugh, cry, by silly, or really do whatever you want because no one (but your photographers!) will be there to witness it.
It won't ruin "the moment".
I promise you that walking down the aisle towards your groom will be just as special and emotional, even if you have seen each other first!
The lighting isn't the best.
First looks are often done in mid afternoon to give enough time to do any portraits, and then hide away as your guests arrive. This is not an ideal time for lighting, and some of the spots you may have in mind for portraits will not have flattering lighting at this time. You will need to shoot in shade so if you know that your venue doesn't have any shade, you may want to either plan to do a first look at another location, or not do a first look. That being said, in all of the weddings I've shot, there has only been one location where there was literally no where with shade for the first look and we had to do it in full sun. So, odds are I can find somewhere beautiful with nice lighting.
First look or not, please, please plan out 10-15 minutes in the last hour before sunset for couples portraits! It's when the lighting is the best, and most photographers prefer to shoot. This is when you can go out in those vineyards or down to the beach and have photos in the gorgeous scenery of your venue while still having flattering lighting for portraits.
It's not traditional.
You may find that older relatives are disappointed that they don't get to see your faces as you see each other for the first time. However I am a firm believer in doing whatever you want because it's YOUR wedding, so please don't let relatives sway you into not doing a first look if you want to. Also, some couples just really want the first time they see each other to be walking down the aisle, and if this is the case for you don't compromise on that either!
Well that's my two cents on the matter! Most importantly, talk to you photographer about it before you make a decision. Every photographer will have an idea how long each portion of a wedding will take them to photograph. You may have chosen a more documentary style photographer who only needs 10-15 minutes for couples portraits, or one who wants 45 min for portraits of just the two of you. Every photographer and couple is different so it's just a matter of figuring out what works best for all of you. No matter if it's before the ceremony or walking down the aisle, it's bound to be an amazing and special moment!