Totally valid question by the OP.
Advantages: If you camp out in front of Apple Store in NYC on Fifth Avenue and are first in line, you will be interviewed by local and possibly national media. If you are wearing an advertisement at that time (say in the form of a t-shirt with the name of your product or URL) you will get "free" press worth potentially hundreds of thousands of dollars. If you camp in front of other stores there is the chance of similar media attention but to a lesser degree.
Then you will be the first person into the Apple store on the morning of April 10 to go play with the Watches that are lined up on the tables. You might need an appointment to get a fitting or individual attention, but there will be something for walk-ins to do.
The first advantage might be worth it to someone. The second advantage doesn't seem worth it to anyone. But maybe if you fear that the Watch is going to sell out in pre-order, but you can't make up your mind, you want to run in there early on April 10 and then pre-order after you can see it.
Since the stores are open 24 hours in many places. I guess you could be in the Apple Store at midnight, maybe they will have the watch section behind a screen or curtain and they will lift it at midnight. That sounds like madness. But then you could take a quick look at the watches, pick one out, and preorder from a computer at the store even without an appointment.