From AP: This is the Google Pixel 2 XL

They're much less necessary on metal bodied phones.

I usually get them for gripping purposes as I find cell phones to be a little too thin these days. My 6P has always been in a slim-fitting case. Just feels better in my hand that the slippery sides it normally has.
 
Yes, the S8 is a 5.8" 18.5:9 display and this is a 6.0" 2:1 display. It's going to be a little taller and since it doesn't have those terrible edge display sides, also slightly wider. Very minimal difference though for overall size.
Thank you!