Stereo speakers plus being louder than previous iPhones is the main reason I will be buying it. It'll be nice not having to lug around a bluetooth speaker everywhere.
It will be handy for those times I listen to podcasts around the house doing boring stuff and my iPad isn't to hand. Use my iPad Pro for that mostly, pretty much the main reason I upgraded from an Air 2, and I wasn't disappointed.
I love it!! There are times I am sitting outside at the table, maybe just walking around without headphones around the house, or sitting on the couch watching videos and I love that this will be available. Some may scuff. Oh well. I was certainly happy about this!!
Louder speakers is also a big deal for moms who walk around in public using speakerphone for their private conversations.
Seriously though. A front facing speaker is a big deal. I started using my iPad Pro a lot more at home because I can finally hear the sound of the YouTube shows. So it would be nice to have a similar sound improvement on the phone. (Hopefully the watch gets a boost too because that speaker is unusable)
When I went from the iPad Air 2 to the iPad Pro (smaller one), the addition of the speakers on the opposite end of the iPad made a world of difference when watching videos. Before that, I was using a strategically placed sticky note to direct the sound forward.