What's with a Pre-Birthday Shoot?

I haven't had my wedding in a church just yet (formulating plans for that though, maybe in 2 years, IF the budget permits), but I am fully aware that before the wedding, couples go on a pre-nuptial photoshoot. Romantic, dramatic, nostalgic...all those stuff make up the overall impact of the pre-nup pics. The couples use those pics for their wedding's printables like invites, souvenirs ,etc.

And one of the many discoveries that I had when I started my party planning frenzy was that kiddie events also have their own version of a 'pre-nup shoot'!